This article is about the mathematical description, analysis and background of the simulation environment SIMULINK. This simulation environment is a well-known tool in applied mathematics and a wide range of fields in engineering, mainly control engineering. SIMULINK is driven by control engineering which is recognisable in the block oriented structure as well as in the notation and characterisation of simulation models. This article will give an overview about the mathematics behind the simulation models in SIMULINK and discuss several items. The structure of the article starts in the beginning with the mathematical definitions and context. A relation between the mathematical aspects and the situation in the simulation environment is given.