Not necessarily. It's not that dissimilar from other pump and dump schemes orchestrated by private parties who buy a bunch of a cheap stock and then use various media channels to try to get others to buy the stock to get it to go up and then sell. The dividing line typically is whether it is an individual entity or multiple entities, and whether it is a coordinated event among multiple entities. It is legal if it is one entity doing it, or multiple entities doing it independently without knowledge of others doing it. Broadcasting the intentions on any type of media is where it gets into a very gray area because it is no longer a single entity or multiple entities doing it independently. It is not known if the people on Reddit bought the stock before or after they announced their intentions; if it was before, then it is probably not legal. "Investment houses" (let's not generically call them "hedge funds" because hedge funds hedge their bets to take bigger risks but also limit their losses) cannot legally coordinate an effort like this with other investment houses; that's where it becomes illegal because that is market manipulation. What's the difference between two investment houses in a coordinated effort (which is illegal) and 200,000 individuals coordinating an effort on Reddit? Both have the same buying power, and both are attempting to manipulate the market for profit. One thing to note, most people who work for investment houses and have access to financial and market information are typically barred from owning individual stocks. A family friend of mine founded and was managing partner of a financial consulting firm that valued stocks and sold that information to investment firms; when he sold the company he said, "Now I can finally become an investor." He couldn't own stocks because of a potential conflict of interest, and that is the case with most people who work at those firms. Individuals who work at those firms are not directly profiting from it; it may affect their bonuses, but it could also cost them their jobs. The other problem is individuals who are buying the stock without access to/knowledge of what is being broadcast on Reddit. If they miss a sell signal from the coordinated effort, then they are the ones left holding the bag. This does not just affect big investment houses; this can also cost individuals (just like every market crash in history). Big losses on one investment lead to selling another... which leads to more losses, and more selling, and that's how crashes start. Also, big investment houses aren't the only ones shorting stocks; individual investors do that too.