  I give an overview of rare event simulation techniques to generate dynamical
pathways across high free energy barriers. The methods on which I will
concentrate are the reactive flux approach, transition path sampling,
(replica-exchange) transition interface sampling, partial path
sampling/milestoning, and forward flux sampling. These methods have in common
that they aim to simulate true molecular dynamics trajectories at a much faster
rate than naive brute force molecular dynamics. The advantages and
disadvantages of these methods are discussed and compared for a simple
one-dimensional test system. These numerical results reveal some important
pitfalls of the present non-equilibrium methods that have no easy solution and
show that caution is necessary when interpreting their results.
