The document discusses five types of professional learning networks (PLNs) that teachers can use: 1) casts such as podcasts and vidcasts, 2) social networks like Facebook and Ning groups, 3) blogs, 4) microblogging via Twitter, and 5) social bookmarking sites like Pinterest and Diigo. Examples are provided for each type to illustrate how teachers can connect with others, share resources and lessons, and expand their knowledge through participating in various online PLNs.