There’s nothing quite like reliving your childhood with your favorite retro games, but are emulators and ROMs legal? The internet will give you a lot of answers, but we talked to a lawyer to get a more definitive answer.

Emulators are legal to download and use, however, sharing copyrighted ROMs online is illegal. There is no legal precedent for ripping and downloading ROMs for games you own, though an argument could be made for fair use.

To find out, we asked Derek E. Bambauer, who teaches Internet law and intellectual property at the University of Arizona’s College of Law. Unfortunately, we discovered that no definitive answer truly exists, since these arguments have yet to be tested in court. But we can at least bust some myths that are floating around out there. Here’s what you need to know about the legality of emulators and ROMs in the United States.

Emulators Are Almost Certainly Legal

Let’s start with the easy stuff. Despite what you may have heard, there’s not a lot of question as to whether emulators themselves are legal. An emulator is just a piece of software meant to emulate a game system—but most don’t contain any proprietary code. (There are exceptions, of course, such as the BIOS files that are required by certain emulators to play games.)

But emulators aren’t useful without game files—or ROMs—and ROMs are almost always an unauthorized copy of of a video game that’s protected by copyright. In the United States, copyright protects works for 75 years, meaning no major console titles will be public domain for decades.

But even ROMs exist in a bit of a grey area, according to Bambauer.

The Possible Exception for ROMs: Fair Use

To begin: downloading a copy of a game you don’t own is not legal. It’s no different from downloading a movie or TV show that you don’t own. “Let’s assume I have an old Super Nintendo, and I love Super Mario World, so I download a ROM and play it,” said Bambauer. “That’s a violation of copyright.”

That’s fairly clear cut, right? And it more or less aligns with the language regarding ROMs on Nintendo’s website, where the company argues that downloading any ROM, whether you own the game or not, is illegal.

But is there a legal defense? Possibly, if you already own a Super Mario World cartridge. Then, according to Bambauer, you might be covered by fair use.

“Fair use is a fuzzy standard, not a rule,” Bambauer explained. He says he could imagine a few possible defensible scenarios. “If I own a copy of Super Mario World, I can play it whenever I want,” he notes, “but what I’d really like to do is play it on my phone or my laptop.” In this case, downloading a ROM could be legally defensible.

“You’re not giving the game to anybody else, you’re just playing a game you already own on your phone,” said Bambauer. “The argument would be there’s no market harm here; that it’s not substituting for a purchase.”

Now, this isn’t black and white; just a potential legal argument. And Bambauer is quick to admit it’s not a perfect one.

“This is by no means a slam dunk argument,” said Bambauer, “But it’s by no means a silly one.” After all, Nintendo could argue that by emulating the game on your phone, instead of buying their official port of a game, they’re losing money.

But, while there is no precedent specific to gaming, there is in other markets. “In the music industry, everyone accepts that space shifting is legal,” Bambauer notes. You can see where this gets complicated.

What If You Rip Your Own ROMs?

A common argument online is that extracting a ROM from a cartridge you own is perfectly legal, but downloading ROMs from the web is a crime. Devices like the $60 Retrode let anyone extract a Super Nintendo or Sega Genesis game over USB, and state their legality over downloads as a key selling point. After all, ripping a CD you own with iTunes or other software is broadly considered legal, at least in the United States.

So is ripping a ROM you own any different than downloading one? Probably not, says Bambauer: “In both cases what you’re doing is creating an additional copy.”

Now, Bambauer could imagine constructing an argument about how one is different than the other, and he admits the optics are different. But he doesn’t think the two situations are all that distinct, legally speaking.

“I think if the argument is, if I were a skilled engineer, I could extract this and have a copy,” said Bambauer. “If we assume, for a moment, that if I did that it would be fair use, then it shouldn’t be different.”

Sharing ROMs Is Unambiguously Illegal

This fair use argument is potentially very wide reaching, but there are limits. “The trouble comes when it’s no longer just me having a copy, it’s giving other people a copy,” said Bambauer.

Consider the entertainment industry. The RIAA and MPAA have found more luck going after the sites and people sharing music, rather than the downloaders. For ROMs it largely works the same way, which is why sites that share games are so frequently shut down.

“Once you’re distributing a ROM, most of the people downloading it probably don’t have legal copies of the game,” said Bambauer. “Then it is market harm, because Nintendo should be able to sell to those people.”

Because of this, it might be a good idea, even if you own a game, to avoid downloading ROMs from peer-to-peer networks, where you’re sharing a copy of the game as you download it.

What If a Game Isn’t Currently On the Market?

Many people argue online that if a game isn’t currently available on the market, downloading a ROM is legal. After all: there can’t be market harm if a game is not currently for sale in digital form.

That argument might not be airtight, according to Bambauer.

“On the one hand, there’s no amount of money that will let me get a legal copy of this game,” said Bambauer. “On the other side of the argument, there’s what Disney does.” Disney’s strategy is to put classic movies “in the vault” for extended periods. Instead of leaving films constantly on the market, they periodically re-release them, which builds up demand and increases sales when that release actually comes.

Video game companies could argue they’re doing the same thing with currently unreleased games, and that ROMs are driving down the potential market value. “It’s a close case,” says Bambauer, “and hasn’t been tested a lot.” But they could make that argument.

At the same time, he notes, a game not currently being on the market could potentially be a useful part of a defense, particularly if you’re downloading a game you already own.

“I couldn’t buy a copy anyway, and I already own a copy,” said Bambauer, again hypothetically. “So it’s kind of like owning a CD, and ripping it on my own.”

All of This Is Mostly Hypothetical

You’re probably starting to see a pattern here. ROMs are such a grey area because there are potential legal defenses on both sides—but no one’s truly tested these arguments before. Bambauer couldn’t point to any case law specifically about video game ROMs, and was mostly just extrapolating from other areas of Internet copyright law.

If one thing is clear, though, it’s this: if you don’t own a legal copy of a game, you don’t have any right to download it (yes, even if you delete it after 24 hours, or other such nonsense).