A new computer language has been designed to describe general types of reactions. These descriptions are used to generate the specific reactions in complex reaction systems. A wide range of reaction networks may be represented using the commands in the reaction description language (RDL). The reaction types are defined by using a sequence of commands to locate the reaction site, manipulate the reactant to form the product, and to prune the reaction network. The syntax of the language was designed to mimic the way reactions are normally described. Therefore, debugging a program written in RDL is simply a matter of proofreading. Optimization methods are employed, transparent to the user, to reorder inefficient reaction descriptions. Reaction types may be easily added, deleted, and modified to adjust the level of detail within a specific reaction network.