Over the past decade, computational modelling, which enables extensive use of mathematics for solving complicated problems, has emerged as a powerful and important tool to predict the micro structure evolution in various casting and solidification processes. The significant advances of numerical modelling techniques have made it possible to analyze transport phenomena, including heat, mass and momentum transfer in the mushy zone during solidification to a high level of detail, leading to the development of various models of microstructure evolution in solidification of alloys. Recently, cellular automaton models have generated significant interest among researchers because of its potential to be applied in practical casting and solidification problems. In this chapter, we will describe the numerical algorithms of cellular automaton models and also show some examples how to put CA models into practical usage.