This chapter of the Handbook of Chemical Reactors describes approaches to the parallelization of reactors with the aim of increasing the efficiency of testing procedures, reducing the time and financial expenditure for testing, increasing the reproducibility of the results, and generating knowledge. Like any experimental procedure, high-throughput experimentation also requires very careful planning of the experiments in the sense of a Design of Experiment (DoE). In the high-throughput workflow, the primary and secondary screening phases are then run through until a corresponding development goal has been achieved. Practically all conventional reactor types can be parallelized. The highest principle in the planning and development of multireactor systems is a completely similar behavior of all reactors of the parallel system, so that a comparability of the results is given. In the stage of realization of a parallelization concept, the reactor system must therefore always be validated against conventional systems. Examples of parallel reactor concepts from the areas of microstructured high-throughput reactors, parallel tubular reactors, parallel batch reactors, and photochemical parallel reactors are presented.