At this year’s annual Berkshire Hathaway meeting in Omaha, ­Warren Buffett, the high priest of value investing, uttered words that would have been grounds for excommunication if they had come from anyone but him.

Buffett began his career nearly 70 years ago by investing in drab, beaten-up companies trading for less than the liquidation value of their assets—that’s how he came to own Berkshire Hathaway, a rundown New England textile mill that became the platform for his investment empire. Buffett later shifted his focus to branded companies that could earn good returns and also to insurance companies, which were boring but generated lots of cash he could reinvest. Consumer products giants like Coca-Cola, insurers like Geico—reliable, knowable, and familiar—that’s what Buffett has favored for decades, and that’s what for decades his followers have too.

Now, in front of roughly 40,000 shareholders and fans, he was intimating that we should become familiar with a new reality: The world was changing, and the tech companies that value investors used to haughtily dismiss were here to stay—and were immensely valuable.

“The four largest companies today by market value do not need any net tangible assets,” he said. “They are not like AT&T, GM, or Exxon Mobil, requiring lots of capital to produce earnings. We have become an asset-light economy.” Buffett went on to say that Berkshire had erred by not buying Alphabet, parent of Google. He also discussed his position in Apple, which he began buying in early 2016. At roughly $50 billion, that Apple stake represents Buffett’s single largest holding—by a factor of two.

At the cocktail parties afterward, however, all the talk I heard was about insurance companies—traditional value plays, and the very kind of mature, capital-intensive businesses that Buffett had just said were receding in the rearview mirror. As a professional money manager and a Berkshire shareholder myself, it struck me: Had anyone heard their guru suggesting that they look forward rather than behind?

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There is a deep and important debate going on in the investment community, one with profound repercussions for both professional money managers and their clients. Some believe that Buffett is right—that we have become an asset-light economy and that value investors need to adapt to accommodate such changes. Noted value managers like Tom Gayner of Markel Corp. and Bill Nygren of Oakmark Funds, for instance, count companies like Amazon and Alphabet among their top holdings. The fact that these stocks often trade at above-­market valuations—a factor that once scared away orthodox value investors—hasn’t deterred them, because the companies’ futures are so bright that they’re worth it.

Other value managers like David Einhorn at Greenlight Capital and Bruce Berkowitz at Fairholme are betting on the very same old-economy companies that Buffett long favored. Berkowitz, Morningstar’s domestic equities Manager of the Decade from 2000–10, has seen his performance suffer this decade, thanks to positions in AT&T and, most notably, Sears Holdings, which declared bankruptcy earlier this fall. Einhorn’s performance has also suffered; his largest position is GM, and he says he has been short what he calls a “bubble basket” that includes Tesla, Netflix, and Amazon.

All value investors continue to agree that price is an important component of value—that’s why we’re called value investors. What’s happening now is a debate about what the drivers of value are—of what constitutes value in the 21st-century economy—and what will drive both the economy and the market forward over the next generation.

Value investors are just that—we hunt for value, and our focus on price in relation to a business’s value makes us easily distinguishable from other investors. Momentum investors, for example, care about price only insofar as they can sell whatever they’ve bought to someone else at a higher one—the so-called greater-fool approach. Then there’s growth investing, in which price takes a distant second place to a business’s prospects for rapid expansion. Because weighing price vs. value is paramount in value investing, those in this school have a reputation of being long-term-oriented, self-denying cheapskates.

The father of value investing was Ben ­Graham, who gave birth to it roughly 100 years ago, when 100% of the components of the Dow Jones industrial average were just that—industrials. Hard assets were what drove companies like Anaconda Copper and National Lead. Consumer marketing was in its infancy; in 1915, the closest thing the Dow had to a consumer products company was General Motors (or maybe American Beet Sugar).

The year before, Graham had graduated second in his class from Columbia University with such a gifted intellect that he was offered teaching positions in three departments: philosophy, mathematics, and English. Acquainted with poverty at an early age, however, Graham chose a career in finance. The market of his day was dominated by tipsters, schemers, and speculators; stock operators trying to corner the market in United Copper had caused the Panic of 1907, which wiped out Graham’s widowed mother’s savings. Graham loathed such speculations, but he was attracted to the upside of equities. He saw them for what they were: a fractional ownership of a company’s business.

Driven by both his academic temperament and practical necessity, Graham set about trying to figure out a predictable, systematic way to make money in stocks. For an answer, he turned to corporate financial statements and the tangible assets represented therein. Graham saw that while equities went up and down in the short run according to the whims of the market, a company’s tangible assets—its forges and its foundries and the inventory they produced—had a solid, knowable value. Graham began to calculate that value in a precise, mathematical way. He asked himself: What would a company be worth if it were to liquidate its assets and pay off its liabilities? Sometimes the liquidation would actually occur; other times it would be a theoretical exercise that gave Graham what he termed a “margin of safety” when buying a security.

By quantifying value and then juxtaposing it with price, Graham found he could make sense of markets. Thus was born security analysis and, with it, value investing.

From the beginning, value investing focused on the quantitative and tangible aspects of a business. Graham was an intellectual who lived in abstractions; he didn’t want to know about the products the companies made. Irving Kahn, one of Graham’s assistants, told Buffett biographer Roger Lowenstein that if someone began to describe to Graham what a company actually did, he would get bored and look out the window. With his focus on liquidation value, Graham tended to buy boring, beaten-down businesses—cigar butts, they came to be known, good for only a few extra puffs. Walter Schloss, a Graham analyst who later became a legendary value investor in his own right, once pitched Graham on Haloid, which owned the rights to a promising technology that would one day become the Xerox machine. While there is no record as to whether Graham looked out the window, he nevertheless said no.

“Walter,” he said, “it’s just not cheap enough.”

One of Graham’s acolytes was a young man from Omaha who was born into the Depression but came of age during America’s large, optimistic postwar expansion. As a teenager, Warren Buffett tried to understand the stock market by studying charts and other technical indicators; when he came upon Graham’s writings, he said that he felt “like Paul on the road to Damascus.” Buffett came East for business school to study under Graham, who by then was teaching at Columbia, and he briefly worked for Graham after graduation. The classic middle-American boy, however, Buffett soon quit New York for his beloved hometown.

Surveying the economy of the mid-1950s with his own partnership, Buffett saw that it was vastly different from the one Graham had encountered as a young man. While the Dow Jones industrial average was still dominated by industrials, it also contained Procter & Gamble, Sears Roebuck, and General Foods. These companies were fundamentally different from an industrial company: The primary driver of their business value had little to do with hard assets. Rather, the value had to do with the company’s brands—with the loyalty and familiarity that customers felt for Ivory Soap and Jell-O gelatin. These emotional ties, encouraged and cemented by mass marketing, allowed businesses to charge high prices for relatively mundane goods.

The great enabler of such businesses was the rise of national television, which both emanated from and reinforced a culture of homogeneity. Market-leading brands used scale in a very different but no less effective way than manufacturing companies. A beer, shampoo, or cola brand with dominant share could flood the three major TV networks with more advertising than their competition, yet still spend less than the competition as a percentage of absolute sales dollars. This set up a virtuous circle for dominant brands and a vicious circle for those less fortunate. Brands like Budweiser went from strength to strength; strong regional brands like Narragansett beer, once the No. 1 seller in New England, slowly but surely withered away.

Value 3.0 Rules of the Road

Even in an economy transformed by technology, many of Warren Buffett’s principles of value investing apply. Here, some dos and dont’s.

Dos

? Always look for a business with a clear-cut competitive advantage. If you can’t explain to your spouse what makes a company special as a long-term moneymaker, it probably isn’t. Amazon has a stranglehold on e-commerce; Google owns search; Sherwin-Williams, in which my fund owns a stake, dominates brick-and-mortar paint stores. What makes a company able to earn outsize profits over the next generation?

? Try to find companies with a small market share, a huge addressable market, and a large competitive advantage. This was Warren Buffett’s recipe for success with Geico, a once-tiny auto insurer that sold directly to consumers rather than pay agents’ commissions. These traits may be present in GrubHub (pictured above), the first mover in the food-delivery market, which my fund also owns. It has an industry-leading market share yet still has less than a 1% share of all American restaurant meals consumed each year. Still TBD: whether consumers will continue to migrate away from in-restaurant dining, and whether Uber and Amazon will try to eat GrubHub’s lunch.

Don’ts

? As Buffett has said, never confuse a growing industry with a profitable one. One cautionary tale from the 2000s: Vonage, a pioneer in routing phone calls over the Internet. Business exploded over the past decade, but so did competition. Profits for everyone imploded, and the big winner (as is so often the case) has been the consumer. Vonage’s stock has never gotten back to its $17/share IPO price.

Read: The Best Investing Advice for 2019 From Fortune’s Experts

? Avoid businesses whose best days are behind them. This is true even if you’re paying a cheap price relative to current earnings or book value because, in the long run, underlying business quality trumps price. Exhibit A: Sears Holdings looked cheap all the way down until it declared bankruptcy earlier this fall. You can still buy a fractional interest in Sears’s future today for a very cheap price, by the way—36¢ a share, as of this writing.

With the help of his partner Charlie Munger, Buffett studied and came to deeply understand this ecosystem—for that’s what it was, an ecosystem, even though there was no such term at the time. Over the next several decades, he and Munger engaged in a series of lucrative investments in branded companies and the television networks and advertising agencies that enabled them. While ­Graham’s cigar-butt investing remained a staple of his trade, Buffett understood that the big money lay elsewhere. As he wrote in 1967, “Although I consider myself to be primarily in the quantitative school, the really sensational ideas I have had over the years have been heavily weighted toward the qualitative side, where I have had a ‘high-probability insight.’ This is what causes the cash register to ­really sing.”

Thus was born what Chris Begg, CEO of Essex, Mass., money manager East Coast Asset Management, calls Value 2.0: finding a superior business and paying a reasonable price for it. The margin of safety lies not in the tangible assets but rather in the sustainability of the business itself. Key to this was the “high-probability insight”—that the company was so dominant, its future so stable, that the multiple one paid in terms of current earnings would not only hold but perhaps also expand. Revolutionary though the insight was at the time, to Buffett this was just math: The more assured the profits in the future, the higher the price you could pay today.

This explains why for decades Buffett avoided technology stocks. There was growth in tech, for sure, but there was little certainty. Things changed too quickly; every boom was accompanied by a bust. In the midst of such flux, who could find a high-probability insight? “I know as much about semiconductors or integrated circuits as I do of the mating habits of the chrzaszcz,” Buffett wrote in 1967, referring to an obscure Polish beetle. Thirty years later, writing to a friend who recommended that he look at Microsoft, Buffett said that while it appeared the company had a long runway of protected growth, “to calibrate whether my certainty is 80% or 55% … for a 20-year run would be folly.”

Now, however, Apple is Buffett’s largest investment. Indeed, it’s more than double the value of his No. 2 holding, old-economy stalwart Bank of America.

Why? Not because Buffett has changed. The world has.

And quite suddenly: Ten years ago, the top four companies in the world by market capitalization were Exxon Mobil, PetroChina, General Electric, and Gazprom—three energy companies and an industrial conglomerate. Now they are all “tech”—Apple, Amazon, Microsoft, and Alphabet—but not in the same way that semiconductors and integrated circuits are tech. These businesses, in fact, have much more in common with the durable, dominant consumer franchises of the postwar period. Their products and services are woven into the everyday fabric of the lives of billions of people. Thanks to daily usage and good, old-fashioned human habit, this interweaving will only deepen with the passage of time.

Explaining his Apple investment to CNBC, Buffett recalled making such a connection while taking his great-grandchildren and their friends to Dairy Queen; they were so immersed in their iPhones that it was difficult to find out what kind of ice cream they wanted.

“I didn’t go into Apple because it was a tech stock in the least,” Buffett said at this year’s annual meeting. “I went into Apple because … of the value of their ecosystem and how permanent that ecosystem could be.”

If the postwar era was about consumer brands operating at scale, the early 21st century is about what we might call digital platforms. Like the branded enterprises before them, they have the permanence and probability that make for a good long-term value investment. Innovation scholar Carlota Perez has written about how at least five times in Western civilization, new technologies have erupted, gone through a speculative frenzy, and then busted, only to settle down after a shakeout into a long, protracted period of stability. We’ve had the high-tech eruption, we’ve had the frenzy of the dotcom boom, and we’ve had the bust. Now we are in what Jonathan Haskel and Stian Westlake, authors of Capitalism Without Capital, call the “bedding-in” phase.

Unlike branded companies, digital businesses often benefit from network effects: the tendency of consumers to standardize on a single platform, which reinforces both consumer preference and the platform’s value. Because of this, the market shares of these platform companies dwarf those of the consumer products giants; software businesses like these are often characterized by a “winner take all” or “winner take most” dynamic. Combine this with the fact that they require little to no capital to grow, and you have Value 3.0—business ­models that are both radically new and enormously valuable.

“In the past you would’ve needed a tremendous amount of capital to achieve global scale,” says Oakmark’s Nygren, whose top position in his Oakmark Fund is Alphabet, “but these companies have done it just by writing code and pressing ‘send.’ ”

Like their branded predecessors, the platform companies are wisely reinvesting their vast profit streams into not only their core business but entirely new platforms as well. Take Alphabet, which my fund also owns: It began with search, a classic two-sided market in which consumers looking for goods and services are paired with advertisers who want to reach them. Google gained an early edge thanks to a superior search algorithm; with the word “google” now routinely used as a verb, it commands 95% of all mobile search. Google tweaks its algorithm twice a day to maintain its search superiority; meanwhile, the cash flow from this asset-less platform is so abundant that the parent can afford to spend $20 billion a year on research and development. That’s more than the annual earnings of Coca-Cola and American Express combined. It’s going into not only the core franchise but also nascent platforms like YouTube (user-generated video content), Android (smartphone operating systems), and Waymo (driverless cars). None of these businesses earns much now, but they may soon do so, and they are funded entirely by Google’s search platform. Little wonder that Amazon founder Jeff Bezos once told a colleague, “Treat Google like a mountain. You can climb the mountain, but you can’t move it.”

Meanwhile, Bezos has built a mountain or two of his own. As the first big mover in ­e-commerce, he created a network of warehouses and logistics capabilities that now allows him to deliver packages to more than 100 million Prime customers in two days or less. He too has chosen to reinvest Amazon’s profits back into the business in various forms: lower prices for customers, ancillary services like Prime Video, and entirely new industries like Amazon Web Services, which provides outsourced, essential computational “plumbing” for the next generation of digital startups. In its core retail business, Amazon still has only a roughly 5% share of U.S. retail commerce despite being at it for more than 20 years. Amazon’s stock may be overvalued today—but with its dual moats of immense customer loyalty and low-cost provider status, there is no argument that it is very valuable.

As these platform companies create billions in value, they are simultaneously undermining the postwar ecosystem that Buffett has understood and profited from. Entire swaths of the economy are now at risk, and investors would do well not only to consider Value 3.0 prospectively but also to give some thought to what might be vulnerable in their Value 2.0 portfolios.

Some of these risks, such as those facing retail, are obvious (RIP, Sears). More important, what might be called the Media-­Consumer Products Industrial Complex is slowly but surely withering away. As recently as 20 years ago, big brands could use network television to reach millions of Americans who tuned in simultaneously to watch shows like Friends and Home Improvement. Then came specialized cable networks, which turned broadcasting into narrowcasting. Now Google and Facebook can target advertising to a single individual, which means that in a little more than a generation we have gone from broadcasting to narrowcasting to mono-casting.

As a result, the network effects of the TV ecosystem are largely defunct. This has dangerous implications not only for legacy media companies but also for all the brands that thrived in it. Millennials, now the largest demographic in the U.S., are tuning out both ad-based television and megabrands. Johnson & Johnson’s baby products, for example, including its iconic No More Tears shampoo, have lost more than 10 points of market share in the last five years—an astonishingly sharp shift in a once terrarium-like category. Meanwhile, Amazon and other Internet retailers have introduced price transparency and frictionless choice. Americans are also becoming more health conscious and more locally oriented, trends that favor niche brands. Even Narragansett beer is making a comeback. With volume growth, pricing power, and, above all, the hold these brands once had on us all in doubt, it’s appropriate to ask: What’s the fair price for a consumer “franchise”?

To be sure, some of the digital-disruption rhetoric is overdone. Cryptocurrency replacing the bank system? Not likely. David Einhorn’s bearish calls on Tesla and Netflix may well be right, not because the stocks are expensive but because they face rising competition. And for all the hype about autonomous vehicles, they’re not anywhere close to being here—yet. But a lot can change in half a generation. If you google “Easter Day Parade, New York City 1900” and then “Easter Day Parade, New York City 1913” and look at the pictures that appear, you will see that the former has nearly 100% horse-drawn carriages while the latter has nearly 100% horseless carriages—i.e., automobiles. And when driverless cars do arrive, what happens to the auto industry? What happens to the auto-insurance industry—that cuddly, capital-intensive commodity business that value investors love to talk about at cocktail parties?

Long-term investors need to be thinking about such shifts, and they need to position their portfolios in accordance with them rather than against them. Darwin is often misunderstood, says Markel’s Gayner, who counts both Amazon and Alphabet among his holdings. “It’s not survival of the fittest, but those who are most adaptable to change, that make it through.”

Industries to Look at … and Avoid

Some industries are particularly well positioned to benefit both from the drivers of “Value 3.0” (network effects, growth that isn’t capital intensive) and more traditional advantages (wide competitive moats). Here are some industries to watch right now and a couple to be wary of.

ATTRACTIVE

Platform tech It’s difficult to see how Alphabet’s Google subsidiary will lose its 95% market share in mobile search. Advertising on the Internet represents only 30% of total worldwide marketing spending, so Google has room to grow. Likewise, Amazon has only a 5% share of U.S. retail spending; thanks to its network of warehouses and its frictionless customer interface, it possesses powerful competitive advantages.

Aerospace While it’s tempting to be swept away by the might of digital platforms, it’s also true that most business continues to be done in the real world, not the ether. Consider the aerospace industry: It has grown 5% per annum over the past 50 years, well ahead of global GDP, yet 80% of the world’s population still has not yet set foot on an airplane. Add to this the fact that aerospace companies tend to be duopolies or oligopolies, and you have a recipe for powerful economic compounders. Not surprisingly, industrial conglomerates Honeywell and United Technologies (maker of the space suit pictured above) are both taking steps to become more aerospace-focused.

NOT SO MUCH

Autos A cyclical, capital-intensive business that makes commoditized products is a troubled industry to begin with. If driverless cars become a reality, then car sharing is not far behind. Once that occurs, it’s virtually certain we’ll need fewer automobiles. Falling production on a fixed-cost base—look out below.

Insurance Another cyclical, commoditized business with no barriers to entry except capital—which is to say, no barriers at all. Returns on equity in insurance have been in structural decline for 30 years, with personal lines most at risk. Warren Buffett, whose Berkshire Hathaway conglomerate is invested in insurance, has acknowledged that self-driving cars could significantly decrease auto-insurance premiums. Such coverage may join the buggy whip in terms of utility within the next generation.

Adam Seessel, who won journalism’s George Polk Award in 1991, is founder and CEO of Gravity Capital Management. His fund owns positions in some of the companies mentioned here.

A version of this article appears in the December 1, 2018 issue of Fortune, as part of the “2019 Investor’s Guide.”