Header bidding has been great for publishers and, as a rule, tough on sell-side platforms. In this discussion, PubMatic President Kirk McDonald talks about evolution of the programmatic selling model and where his company is making bets. "Header bidding has moved control of ad serving back to the publisher," McDonald says in this episode of AdExchanger Talks. "The evolution is putting publishers back in a place where they're controlling the tension around access to their impressions."