  In the study of rare events in complex systems with many degrees of freedom,
a key element is to identify the reaction coordinates of a given process. Over
recent years, a number of methods and protocols have been developed to extract
the reaction coordinates based on limited information from molecular dynamics
simulations. In this review, we provide a brief survey over a number of major
methods developed in the past decade, some of which are discussed in greater
detail, to provide an overview of the problems that are partially solved and
challenges that still remain. A particular emphasis has been placed on methods
for identifying reaction coordinates that are related to the committor.
