Originally answered Jan 17, 2011
Communities of practice are groups of people who, for a specific subject, share a specialty, role, passion, or a set of problems. Such people make the decision to join communities to deepen their understanding of the subject by interacting on an ongoing basis, asking and answering questions, sharing information, reusing good ideas, solving problems for one another, and developing new and better ways of doing things.
Social networks are collections of people who are acquainted or connected as friends, business contacts, or colleagues and communicate through social software tools. Using functions such as “follow,” “friend,” “like,” connect,” “chat,” or “subscribe,” they create links to one another.
Members of communities of practice are connected by their shared specialty or role. They join and participate in communities to share new ideas, lessons learned, proven practices, insights, and practical suggestions; innovate through brainstorming, building on each other’s ideas, and keeping informed on emerging developments; reuse solutions through asking and answering questions, applying shared insights, and retrieving posted material; collaborate through threaded discussions, conversations, and interactions; and learn from other members of the community and by participating in community events.
Members of social networks are connected by friendship, work relationships, or shared interest. The decision to add someone to one’s social network is usually more casual than to join a community of practice. Social network connections can range from very weak virtual acquaintances to very strong personal friendships. For example, in Facebook, my friends include those from high school, college, my local community, musicians I like, work colleagues, close professional associates, and people who share my passion for knowledge management.
Communities of practice and social networks can have overlapping members. Many people who belong to the same communities as I do are also connected to me in LinkedIn, Facebook, Twitter, Quora, etc.