Networks and Communities: Patterns of Connections in Complex Systems (Research Seminar, October 14th, 2004) Mark Newman Center for the Study of Complex Systems University of Michigan Abstract Many complex systems can be usefully represented as networks, such as social networks, computer networks, and information networks. In recent years researchers have performed some impressive empirical studies of these systems which have yielded large volumes of complex network data, and we have been using these data to probe the structure of networked systems, focusing particularly on the way the systems subdivide into groups or communities of nodes. In this talk I will discuss a variety of methods we have developed for probing community structure