RANKED: The 37 hottest pre-IPO ad tech startups of 2016

But the private ad tech market is still bustling. Plenty of ad tech companies are getting snapped up by larger firms, raising VC money (although, admittedly, some of the rounds aren't as big as they used to be), or simply steadily growing their businesses quarter-on-quarter.

Three of the companies on last year's ad tech startup ranking have since been acquired.

This ranking (and, yes, we were debating whether to lose the "pre-IPO" headline) looks at the hottest private ad tech companies right now.

Our data comes from CrunchBase, LinkedIn, our own reporting, that of other business publications, and the advice of a handful of ad tech industry insiders.

Our ranking takes into account: Revenues, headcount, venture funding, recent news, whispers, and reputation. Last year's ranking was more weighted toward revenue, whereas this year's ranking takes into account more metrics than revenue alone. (One company in the list is even pre-revenue!)

See our methodology at the end.