  Diseases spread over temporal networks of contacts between individuals.
Structures of these temporal networks hold the keys to understanding epidemic
propagation. One early concept of the literature to aid in discussing these
structures is concurrency -- quantifying individuals' tendency to form
time-overlapping "partnerships". Although conflicting evaluations and an
overabundance of operational definitions have marred the history of
concurrency, it remains important, especially in the area of sexually
transmitted infections. Today, much of theoretical epidemiology uses more
direct models of contact patterns, and there is an emerging body of literature
trying to connect methods to the concurrency literature. In this review, we
will cover the development of the concept of concurrency and these new
approaches.
