Inspired by these observations many researchers have proposed models of networks that typically seek to explain either how networks come to have the observed structure or what the expected effects of that structure will be. The largest portion of this review has been taken up with discussion of these models, covering random graph models and their generalizations (section 4), Markov graphs (section 5), the small-world model (section 6), and models of network growth, particularly the preferential attachment models (section 7).