The document discusses 16 design patterns for using game mechanics to create user engagement in social web applications. It covers patterns for attracting first-time users ("Come and Try It") like visual storytelling, tutorials, and reward schedules. Patterns for building community ("Bring Your Friends") include forming teams, social feedback, and sharing milestones. Patterns for repeat visits ("Come Back") consist of advanced user paths, content unlocks over time, quest queues, and using scarcity and time pressure. The document stresses measuring the effects of these patterns and iterating based on metrics.