The digital ad industry is scrambling as consumer anti-tracking policies from big tech companies like Google and Apple and privacy regulations across the world have already started to wipe out ad revenue.
By one estimate, Apple's 2021 app tracking privacy change alone was expected to erase $16 billion in revenue from the world's biggest digital ad companies last year.
"As every year progresses, it's much more of an existential issue for the ad industry than the year prior," said Anthony Katsur, CEO of IAB Tech Lab, an ad industry trade group.
These companies were selected based on Insider's own reporting, input from ad industry experts, and data from Sincera, an analytics company that tracks which adtech companies are most used in the industry.
This list does not include the big tech companies like Google and Amazon.