Berkshire Hathaway (BRK-A) (BRK-B) was a struggling textile company when Warren Buffett first invested in it in 1962.

Today, it’s a $400 billion behemoth. In Buffett’s own words, it’s a “sprawling conglomerate, constantly trying to sprawl further.”

The companies in Berkshire’s portfolio vary greatly. But one thing ties them all together: Buffett says they’re about “maximizing long-term capital growth.”

Here’s a brief introduction to Berkshire Hathaway.

The insurance business is the backbone of the company

After it acquired National Indemnity in 1967, Berkshire relied on its insurance businesses to power much of its expansion.

As Berkshire has gotten bigger and diversified its businesses, its insurance operations have become a smaller contributor to earnings than in the past, currently making up 26% of total company earnings. But they remain an important part of the company’s access to a permanent capital base by generating what’s known as “float.”

Berkshire Hathaway Chairman Warren Buffett talks in front of a mock BNSF railroad engine. REUTERS/Rick Wilking More

“Float” is money collected up front that is not paid out until later. In Berkshire’s property & casualty (P&C) insurance businesses, premiums are collected up front, but claims are paid out often years or decades later, allowing the float to be used for investments.

Today, Berkshire’s insurance group consists of four segments: GEICO (auto insurance), General Re (reinsurance), BH Reinsurance Group (retroactive reinsurance through subsidiaries), and BH Primary (focused on commercial markets, led by National Indemnity Co).