Once upon a time, a startup valued at more than $1 billion was a rare thing indeed. Now, according to data from the Wall Street Journal, it seems increasingly commonplace, with some 73 venture-backed startups currently valued at more than $1 billion. Those companies include Uber ($41.2 billion), Palantir ($15 billion), SpaceX ($12 billion), Airbnb ($10 billion), and Snapchat ($10 billion). More than 20 of them are headquartered in San Francisco; five are in New York; and four take up space in comparatively tiny Palo Alto. Top investors include Sequoia Capital (which has poured money into 17 billion-dollar startups), Kleiner Perkins (an investor in 14 startups), Tiger Global (12 startups), T. Rowe Price (11 startups), and Andreessen Horowitz (also 11 startups). Check out the latest startup jobs. As noted by the Journal, the number of startups crossing that billion-dollar mark has nearly doubled year-over-year. Or as Fortune summed it up last month: We are in the Age of Unicorns, where the billion-dollar startup is practically blasé; investor firms are now interested in those firms capable of reaching a $10 billion valuation. Valuation, of course, has nothing to do with the startup’s revenue or utility to the broader world. Few of these startups earn enough in revenue to justify such stratospheric estimates, and it’s hard to argue that a company that specializes in self-destructing text messages (Snapchat) is nearly as valuable from a macroeconomic perspective as a company that launches rockets into space (SpaceX). Rather, valuation is all about potential: when investors shovel millions of dollars into these firms, they’re betting on future growth and the potential for disruption. If Uber remolds how the world transports people and goods, or if Airbnb undermines the traditional hotel market, they’ll more than justify their ephemeral price tag. But for every company that succeeds on that level, a handful might fail—and take those illusory billions with them. Image: isak55/Shutterstock.com