In order to illustrate the use of CFD to provide an understanding of mixing processes, three examples, mixing in a pipe, homogenization with a static mixer and the flow in a mixing vessel with a rushton turbine, are discussed and compared to experimental results. Special interest is focussed on the subsequent concentration distribution, which is closely linked to the turbulent properties. A semiempirical model is presented for a quantitative prediction of the initial turbulent conditions. Using special numerical techniques the mixing vessel with wall-seperated baffles, which is a problem generally considered beyond the capabilities of numerical codes, can be simulated.