This chapter deals with single-component fluids, i.e. pure fluids not being mixed with other fluids. In Part I idealised single-component fluids have already been introduced: Ideal gases, that follow the well-known thermal and caloric equations of state, and incompressible liquids, whose specific volume remains constant. For incompressible liquids the caloric equations of state can be adapted easily. The behaviour of real fluids, however, deviates from the idealised models. In particular, real fluids can change their state of aggregation.