In this paper, we present different methods of simulating AO systems, and show how these simulation tools have evolved in the last
years. The evolutions have been driven by new projects (like more complex MCAO systems) and new telescopes (especially ELTs).
These developments have been made in several directions: increasing simulation speed, complexity (more effects taken into account)
and integrating the latest developments in algorithms.
We will also discuss new directions in simulations, like new applications and new ways of estimating AO system performance.