Abstract Motivation: Only models that are accessible to researchers can be reused. As computational models evolve over time, a number of different but related versions of a model exist. Consequently, tools are required to manage not only well-curated models but also their associated versions. Results: In this work, we discuss conceptual requirements for model version control. Focusing on XML formats such as Systems Biology Markup Language and CellML, we present methods for the identification and explanation of differences and for the justification of changes between model versions. In consequence, researchers can reflect on these changes, which in turn have considerable value for the development of new models. The implementation of model version control will therefore foster the exploration of published models and increase their reusability. Availability: We have implemented the proposed methods in a software library called Biochemical Model Version Control System. It is freely available at http://sems.uni-rostock.de/bives/. Biochemical Model Version Control System is also integrated in the online application BudHat, which is available for testing at http://sems.uni-rostock.de/budhat/ (The version described in this publication is available from http://budhat-demo.sems.uni-rostock.de/). Contact: [email protected]