Facebook is a social networking website that allows users over 13 to create profiles, add friends, send messages and update statuses. Users can also join networks by workplace, school or interests. Twitter is a microblogging service that allows users to send and read tweets, which are text posts up to 140 characters. LinkedIn is a professional networking site where users can make professional connections, join industry groups and interact with other professionals. Social media provides a free and global way for users to engage in conversations around shared content, though businesses should monitor return on investment of time spent on different platforms.