 We review a selection of methods for performing enhanced sampling in molecular dynamic simulations. We consider methods based on collective variable biasing and on tempering, and offer both historical and contemporary perspectives. In collective variable biasing, we first discuss methods stemming from thermodynamic integration that use mean force biasing, including the adaptive biasing force algorithm and temperature acceleration. We then turn to methods that use bias potentials, including umbrella sampling and meta-dynamics. We next consider parallel tempering and replica exchange methods. We conclude with a brief presentation of some combination methods. This article was authored by Cameron Abrams and Giovanni Bussi.