The document discusses tagging and its advantages over categorization for organizing information. It begins by comparing tagging on a personal level versus social systems formed by tagging. It then outlines some weaknesses of tag-based social systems and proposes nine design principles for tagging systems, such as making the system personally useful, identifying a symbiotic relationship between personal and social tagging, and enabling serendipity. The document advocates for keeping input simple through tagging while still supporting different approaches like faceted browsing and recommendations.