This book examines the fact-checking strategies adopted by major platforms such as Meta, X, TikTok, and YouTube to combat misinformation, including third-party verification, AI tools, community-based systems, and government initiatives. Drawing on survey data and expert interviews from the US, Nigeria, India, and Lithuania, the study finds that human-led approaches are generally more trusted than AI or government-driven methods, particularly when transparency and independence are emphasized. The research highlights the trade-offs platforms face between content integrity and engagement, and calls for more transparent, inclusive, and psychologically informed fact-checking systems to strengthen credibility online.