This document discusses different types of online communities and their defining characteristics. It identifies six main categories of communities: communities of practice focused on shared professional skills; communities of interest for sharing information on a common topic; communities of purpose for accomplishing specific tasks; communities of inquiry for collaborative problem solving; communities of inspiration focused on discovery; and communities of innovators seeking to drive new ideas and reforms. Each community type is defined by its purpose and incentives for participation, with examples given of existing communities that fall into each category.