Header bidding is a technological solution in programmatic advertising which was developed as a response to the traditional waterfall model. The waterfall model brings together a few ad networks in a serial connection. Firstly, the opportunity to place ads is given to the network with the highest priority (with conditions such as minimal CPM).
If that network does not have an ad ready the opportunity is given to the next network and so on. The main advantage of header bidding is that it gives the opportunity to a potentially unlimited number of networks to compete for every impression simultaneously, which results in higher CPM rates and more profit for web publishers. Header bidding has its advantages and disadvantages.
There are two implementation options - client side (for example prebid.org) and server side (Google Exchange Bidding). The main disadvantage of client side header bidding is that it can cause latency and it is not currently supported by all the relevant Ad Exchanges. Server side header bidding relies on ad server technology which in turn can compromise the basic idea of equal approach for every bidder.Depending on the situation header bidding can be a good solution.