Process model merging receives data representative of a first model that models a first process and a second model that models a second process, and determines, based on the data and a predetermined plurality of basic model manipulation operations, atomic differences in the second model relative to the first model. Compound differences are determined in the second model relative to the first model. A user is informed of the atomic differences and the compound differences. The user is allowed to select a set of the plurality of basic model manipulation operations. A modified first model is obtained by applying the selected set of basic model manipulation operations to the first model.