Retargeting is a marketing strategy that brings back visitors who have shown interest in a brand or its products, with various types including search, site, email, and social media methods. While it typically offers benefits like lower CPMs and higher CTRs compared to traditional ads, it also presents drawbacks such as user discomfort and tracking difficulties. Setting up a retargeting campaign involves careful planning regarding content, duration, frequency, design, and partner selection to enhance effectiveness and avoid common pitfalls.