The announcement of the Inc. 500 every year is one of those events that make you feel that America is a great country. What other response is there to stories like that of David Glickman, whose startup Ultra Mobile tops the 2015 list with growth of 100,849 percent over three years? That record would be astounding enough, but even more remarkably, this is Glickman's second time in the No. 1 spot. He first hit it with Justice Technology in 1998, and he did it the same way both times: by figuring out how to give phone customers a much better deal than the big incumbents do, especially internationally.

Or consider Jessica Mah, our cover subject, who had the guts and wisdom to discard her original product at her financial startup, inDinero, when she realized that customers wanted something different. Second time's a charm: The company has grown nearly 2,700 percent, good enough for No. 146 on the Inc. 500. Mah, Glickman, and the 498 other Inc. 500 honorees are doing what entrepreneurs are supposed to do: take chances, create something new and better, and reap extraordinary growth as a reward. That's how free enterprise is supposed to work.

But the other thing about free enterprise is, you don't get to rest on your laurels for long. Inc. 500- style growth tends to attract elements -- investors and competitors, and sometimes regulators -- that transform the environment in which you operate. By way of example, all three of those forces are converging on alternative finance, an industry that includes inDinero and a host of other Inc. 500 honorees this year. (Senior editor Maria Aspan's "Fintech Finally Lifts Off" tells you why.)

Rapid growth changes startups from within, too. Once you get big enough, your company enters a stage that editor-at-large Leigh Buchanan, in "Your Awkward Phase, and Why You Should Love It," likens to adolescence. At that point, you face a number of grownup choices, including whether the people who brought you this far are the right ones to take you to the next milestone. You may even need a serious conversation about whether you are the right person to get your business to the next milestone. Phil Libin, the co-founder of Inc.'s 2011 Company of the Year, Evernote, and a key source in Leigh's story, had just such an internal heart-to-heart -- and made the hugely grownup decision to replace himself as CEO.

No one said that entrepreneurship is easy, or that your work will stop once you make the Inc. 500. The challenges of adolescence naturally await many of this year's fastest-growing group. But for most, that's in the future. For now, it's Inc.'s extra­ordinary privilege to honor 500 companies that thoroughly capture what makes America great -- to name them, to introduce you to the work they do, and to tell their amazing stories.

From the September 2015 issue of Inc. magazine