In order to illustrate the use of CFD in providing an understanding of mixing processes, three examples, mixing in a pipe, homogenization with a static mixer and flow in a mixing vessel with a Rushton turbine, are discussed and compared with experimental results. Special attention is focussed on the resultant concentration distribution, which is closely linked to turbulent properties. A semi-empirical model is presented for a quantitative prediction of the initial turbulent conditions. Using special numerical techniques a mixing vessel with wall-separated baffles, which represents a problem generally regarded as beyond the capabilities of numerical analysis, can be simulated.