This document summarizes key concepts from two journal articles about social network structures in online communities. It discusses how the flow of information and overall cohesion of online groups depends on their network structure. Some important concepts discussed include social capital, structural holes, brokerage vs closure, and betweenness vs constraint. The first article examines these concepts in the context of the online community Slashdot.org. The second article studies brokerage and closure in the virtual world of the massively multiplayer online game Everquest II.