On the 7thSeptember 2018, industry analyst Karsten Weide (@KarstenW) at IDC published a market share report titled Worldwide Digital Advertising Software Market Shares, 2017: Despite Intense M&A Activity, Ad Tech Still a Fragmented Market (7-Sep-2017, DOC #US44240218).
Criteo is the market share leader.
See also our blog post on this report or check the fireside conversation between Karsten Weide / Programme Vice President Media & Entertainment, IDC and Jen Whelan / SVP Marketing, Criteo on future trends for AdTech.