Here are the 18 hottest adtech companies of 2019

• The adtech industry has grappled with big issues like privacy, shrinking funding, and a shift into TV in 2019.
• Consolidation continued this year, with big companies like Roku and Publicis Media acquiring adtech companies.
• For its annual list of hottest adtech companies, Business Insider identified 18 firms that were best adapting to those challenges.
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2019 was the year the adtech industry was forced to adapt to sweeping new privacy laws and a rapidly changing media business.

Growing concerns about privacy and the death of cookies that fuel digital advertising; the advent of the California Consumer Privacy Act (CCPA) and Europe's General Data Protection Regulation (GDPR); and tech giants Apple and Google clamping down on how marketers use third-party cookies required many adtech companies to change their pitches to marketers.

Amazon's nascent advertising business gained steam with a new cottage industry of e-commerce-minded firms helping marketers use the platform. Adtech firms also had to join the chase for the $70 billion TV-advertising market.

At the same time, it has gotten harder for adtech companies to raise funding as investors look for sustainable business models with recurring and diversified revenue. And Facebook, Google, and Amazon control about 70% of digital-advertising budgets, leaving adtech companies to fight for the scraps.

As a result, 2019 was a year of consolidation. The holding-company giant Publicis bought Epsilon for $4.4 billion. Firms like Dataxu and Placed got scooped up, while other companies like Sizmek, Nanigans, and IgnitionOne sold off for pieces.

As more big companies acquire adtech firms, it's getting harder for independent adtech companies to compete, Karsten Weide, the program vice president of media and entertainment at IDC, said.

"The whole independent advertising ecosystem is really in trouble - they need to diversify," Weide said.

We identified a handful of companies that were best positioned to survive these challenges and thrive in the year ahead.

Methodology

To compile the list, we drew on nominations and talked to analysts, consultants, and investors.

We looked at a number of factors in evaluating companies, such as their revenue, funding raised, and reputation in the industry. We considered the issues the companies were trying to solve, from building technology to modernizing the decades-old TV industry and preparing marketers for privacy legislation and regulation.

We also highlighted one "star to know" from each company. This list includes a mix of roles.

Here are the 18 hottest adtech firms of 2019, listed alphabetically: