Nobody is actually required to file a Form D. Rather, everybody who sells securities in the US is required to either register their offering (basically, be a public company), or find an exemption from registration. The most common exemption for issuers (companies selling shares of their own stock in order to raise money) is 15 U.S. Code u00a7 77d(a)(2), known as Section 4(a)(2) (formerly section 4(2)) of the Securities Act of 1933 u2022 hey, don't ask me how they come up with the section numbers! This says that you don't have to register your stock sale as long as it is not a public offering. As long as you don't publicly solicit investment, you don't have to register or file anything. End of story, but not quite.That's the statute. The regulations implementing the statute are commonly called Regulation D. Among its provisions are three safe harbors, know as Rule 504, 505, an 506. If you comply with any of these, including properly filing Form D, you are deemed not to have made a public offering so your stock sale is okay. As an added bonus, Rule 506 preempts state laws, so if you file a Form D for a 506 sale you don't have to do any state filings.So the answer is, companies don't really have to file a Form D. But it's good practice to file them if they can, because doing so gives them a defensible position that they did not make an illegal public offering, and avoids the need for state filings. The cost is that a Form D filing is a public record, so now everybody knows how and when you raised money (they can also get this from any restated Certificate of Incorporation filed with Delaware, among other records). Sometimes a company wants to be extra private, and if they raise money only from a small group of sophisticated institutional investors who they already know, it's safe to simply rely on complying with Section 4(2) without going through the further step of confirming that with a Form D.