All companies have to start somewhere, and often, it involves having the founders invest a chunk of their own money in the hopes of eventually growing the business. But as small, private companies start to gain traction, many come to find that they need outside financing to continue growing, and therefore decide to go public. And that's where IPOs come in. An IPO, or initial public offering, is the process by which a privately held company begins selling stock to outside investors, thus becoming a public company. From that point on, the company can raise the capital it needs by selling shares, but it must also comply with a strict set of reporting guidelines, as established by the Securities and Exchange Commission (SEC).