MESSAGEix is a versatile, dynamic, model framework for energy-engineering-economy-environment (E4) systems research.

MESSAGE (without “…ix”) is a specific formulation of a generic linear programming (LP) optimization model for strategic energy planning and integrated assessment of E4 systems, developed by the IIASA Energy, Climate, and Environment (ECE) Program since the 1980s. To incorporate feedback between prices and demand levels for energy and commodities, the LP model can optionally be linked to the economic general equilibrium (GE) MACRO model.

The message_ix Python package—also fully usable from R—includes:

• Implementations of MESSAGE, MACRO, and their linkage, in GAMS,
• Application programming interfaces (APIs) and tools for model building and scientific programming,
• Extensive documentation and a complete test suite.

The framework is built on IIASA's ix modeling platform (ixmp), which provides data warehouse features for numerical scenario analysis.

Complete documentation of the framework is available at https://docs.messageix.org. This includes:

• Installation and recommended pre-requisite learning. See ‘Getting started’, or the file INSTALL.rst.
• Tutorials that introduce and demonstrate core features of the model framework using simple, single-country models, for both independent and classroom learning. See ‘Tutorials’ or the file tutorial/README.rst.
• The Python and R APIs.
• The complete mathematical formulation of MESSAGE and MACRO, created automatically from inline comments in the GAMS source code.
• How to cite MESSAGEix when using it in published scientific work. See ‘User guidelines and notice’ or the file NOTICE.rst.

Other forms of documentation:

• The online documentation is built automatically from the contents of the message_ix GitHub repository.
• Documentation for the ‘latest’ or ‘stable’ release is shown by default.
• Use the chooser to access the ‘latest’ version, corresponding to the main branch and including the latest development code; or to access docs for a specific release, e.g. v3.2.0.
• For offline use, the documentation can be built from the source code. See the file doc/README.rst

• We aim to create a community that is welcoming to everyone. Please respect our Code of Conduct at all times when interacting with message_ix and the community.
• We warmly welcome all contributions to our community. Please take a look at our guidelines for contributing to development.
• If you are looking to understand how the message_ix team operates and how we decide what to do with your contributions, please read our governance guidelines.
• We highly value code security. To learn more about our security practice and advice, please visit our security policy.
• We strive to entertain a welcoming and inclusive community. If you struggle to use message_ix, please check our guidelines for getting support.
• We also:
  • Host an annual MESSAGEix Community Meeting.
  • Publish, at least once per year, a community newsletter. You are cordially invited to subscribe by filling this form and ticking the box for “MESSAGEix Community”.

Copyright © 2018–2025 IIASA Energy, Climate, and Environment (ECE) Program

The MESSAGEix framework is licensed under the Apache License, Version 2.0 (the "License"); you may not use the files in this repository except in compliance with the License. You may obtain a copy of the License in LICENSE or at https://www.apache.org/licenses/LICENSE-2.0.

In addition and per good scientific practice, you must cite the appropriate publications when you use MESSAGEix in scientific work. Again, see ‘User guidelines and notice’ or the file NOTICE.rst.