  The fitness landscape encodes the mapping of genotypes to fitness and
provides a succinct representation of possible trajectories followed by an
evolving population. Evolutionary accessibility is quantified by the existence
of fitness-monotonic paths connecting far away genotypes. Studies of
accessibility percolation use probabilistic fitness landscape models to explore
the emergence of such paths as a function of the initial fitness, the
parameters of the landscape or the structure of the genotype graph. This
chapter reviews these studies and discusses their implications for the
predictability of evolutionary processes.
