Header bidding is an advanced advertising technique that broadcasts the programmatic demand to the multiple demand sources in parallel before the DFP call. The programmatic demand is then pushed in DFP to allow multiple exchanges/demand partners to compete against the DFP line items, Google AdX and direct campaigns. Since, in this technique, multiple ad exchanges get to 'see' the impression in real time, they typically respond with a bid and the highest bidder among all the exchanges win the impression.