Network theory is the study of graphs as a representation of either symmetric or asymmetric relations between discrete objects. It studies technological networks (the internet, power grids, telephone networks, transportation networks), social networks (social graphs, affiliation networks), information networks (World Wide Web, citation graphs, patent networks), biological networks (biochemical networks, neural networks, food webs), and many more. Graphs provide a structural model that makes it possible to analyze and understand how many separate systems act together.
This (expanding) collection houses some of the "interesting" networks that are used in research. The description and references for each network can be found on its separate page.