This document discusses taxonomies, folksonomies, and metadata services at MIT Libraries. It provides examples of controlled vocabularies and taxonomies developed for clients. It also discusses the differences between taxonomies and ontologies, and some Semantic Web projects using ontologies. Additionally, it outlines MIT Libraries' efforts to incorporate user tagging and folksonomies through tools like The Virtual Browsery and Facebook apps. Finally, it discusses lessons learned about using taxonomies and folksonomies to improve findability of information resources.