  In this chapter we provide an overview of the current status of the
simulations and modelling of the Cosmic Dawn and Epoch of Reionization. We
discuss the modelling requirements as dictated by the characteristic scales of
the problem and the SKA instrumental properties and the planned survey
parameters. Current simulations include most of the relevant physical
processes. They can follow the full nonlinear dynamics and are now reaching the
required scale and dynamic range, although small-scale physics still needs to
be included at sub-grid level. However, despite a significant progress in
developing novel numerical methods for efficient utilization of current
hardware they remain quite computationally expensive. In response, a number of
alternative approaches, particularly semi-analytical/semi-numerical methods,
have been developed. While necessarily more approximate, if appropriately
constructed and calibrated on simulations they could be used to quickly explore
the vast parameter space available. Further work is still required on including
some physical processes in both simulations and semi-analytical modelling. This
hybrid approach of fast, approximate modelling calibrated on numerical
simulations can then be used to construct large libraries of reionization
models for reliable interpretation of the observational data.
