An interactive simulator of the process of anaerobic digestion was developed. It is based on four interacting submodels describing the biological, physicochemical, reactor, and plant subsystems of the overall process. The simulator was adapted to simulate a 10 L lab-scale reactor processing three different well-defined substrates as well as varying mixtures of these compounds. Because of its structured configuration, the simulator can be adapted to other types of biogas plants with respect to plant setup, reactor volume, and substrate composition. The biological and physicochemical submodels were implemented in the programming language FORTRAN; the reactor and plant submodels were implemented in an industrial process control and simulation program. The combined submodels result in an interactive process simulator that was equipped with various control loops, automations, data acquisition systems, and graphical user interfaces. The simulator can be used for the design, test, and optimization of automation strategies, industrial and academic education, and process optimization. Its application in these three fields can lead to increased biogas and energy yields as well as a stable and safe operation of biogas plants.