Programmatic advertising optimizes the buying and selling of online advertising space through software and algorithms. At the heart of this system is real-time bidding (RTB), where ad impressions are auctioned in milliseconds based on user profiles on ad exchanges. Advertisers use demand-side platforms (DSPs) to bid on these impressions, targeting specific audiences, while publishers employ supply-side platforms (SSPs) to maximize their advertising revenue. The process involves specialized agencies or trading desks, and increasingly, advertisers prefer private agreements for better rates and secure environments. Challenges with programmatic advertising include complexity, inventory quality, fraud, and privacy concerns.