  In these notes we present a pedagogical account of the population dynamics
methods recently introduced to simulate large deviation functions of dynamical
observables in and out of equilibrium. After a brief introduction on large
deviation functions and their simulations, we review the method of Giardin\`a
\emph{et al.} for discrete time processes and that of Lecomte \emph{et al.} for
the continuous time counterpart. Last we explain how these methods can be
modified to handle static observables and extract information about
intermediate times.
