The document discusses header bidding, which allows bids from demand sources to be considered concurrently rather than consecutively within the ad server. This has resulted in increased yields for publishers and more opportunity for clients to access inventory. Publishers are using header bidding successfully by changing demand prioritization, creating opportunities for preferred clients through "biddable guaranteed" setups, and gaining insights into latent demand and yield opportunities. While not a perfect solution, header bidding's impact on the programmatic marketplace is significant and its concept of concurrent decision making will continue to be built upon.