  A practical introduction to stochastic modelling of reaction-diffusion
processes is presented. No prior knowledge of stochastic simulations is
assumed. The methods are explained using illustrative examples. The article
starts with the classical Gillespie algorithm for the stochastic modelling of
chemical reactions. Then stochastic algorithms for modelling molecular
diffusion are given. Finally, basic stochastic reaction-diffusion methods are
presented. The connections between stochastic simulations and deterministic
models are explained and basic mathematical tools (e.g. chemical master
equation) are presented. The article concludes with an overview of more
advanced methods and problems.
