This Practice Note provides an overview of the adtech ecosystem and the programmatic buying and selling of online display advertising. It considers the technologies and transaction processes that power programmatic advertising, the differences between the programmatic transaction types, pricing models, the key participants in the adtech ecosystem and programmatic advertising more generally, and the real-time bidding (RTB) auction process. See also Practice Notes: • Adtech and programmatic advertising—data use • Adtech and programmatic advertising—legal issues • Adtech and programmatic advertising—tracker • Adtech and programmatic advertising—glossary Quick view The table below provides an overview of the topics considered in this Practice Note, with links to the relevant section where more detailed information can be found. Section Overview What is adtech? Adtech (advertising technology) refers to the technologies, software and services used by advertisers and publishers to create, run, manage and optimise digital advertising campaigns, and for the process of buying, selling, delivering and targeting digital advertising. This section considers how adtech is defined, why it emerged and how it can be distinguished from martech. What is digital advertising? Digital