The study of a flow separatmg from the surface of a solid body, and the determination of global changes in the flow field that develop as a result of the separation, are among the most fundamental and difficult problems of fluid dynamics. The phenomenon of separation is often encountered in industrial and engineering applications, such as in heat exchangers and flows over buildings and in geophysical problems, e.g. flows over dunes and grooves. In order to facilitate a better understanding of the separation process as a whole, the separation on a forward facing step in a straight channel was investigated by experimental and computational methods.In the experimental part of the study, different visualisation techniques were used to reveal the basic structure and dynamics of separation and to illustrate the flow states and flow behaviour for low and moderate Reynolds numbers (Re-numbers).