Online ad targeting works primarily through the use of cookies, tracking user behavior across websites. It collects data on users' browsing habits, preferences, and demographics to deliver personalized advertisements tailored to their interests. Ad networks use this information to display relevant ads to potential customers, increasing the chances of engagement and conversion. Additionally, advanced algorithms and machine learning techniques analyze user data to optimize ad placement and effectiveness in real-time, making it a critical component of modern digital marketing strategies. However, this practice raises important considerations regarding user privacy and consent.