This document discusses re-engagement campaigns for mobile apps. It notes that most apps see high dropout rates, with only 22% of downloaded apps opened once and 5% continuing use after 6 months. Re-engagement campaigns aim to reconnect with inactive users through targeted push notifications, emails, and mobile ads. Unlike web ads, mobile ads typically lack user data for customization. The document then outlines how re-engagement suppliers can implement segmented, deep-linked mobile ads using unique user identifiers from app events and real-time bidding exchanges. It stresses the importance of early re-engagement efforts to reduce user acquisition costs and increase user engagement and conversions over time.