CMIP5 represents the most ambitious and computer-intensive model inter-comparison project ever attempted. Integrating a new generation of Earth system models and sharing the model results with a broad community has brought with it many significant technical challenges, along with new community-wide efforts to provide the necessary software infrastructure. This special issue focuses on the software that supports the scientific enterprise for CMIP5, including: couplers and coupling frameworks for Earth system models; the Common Information Model and Controlled Vocabulary for describing models and data; The development of the Earth System Grid Federation; the development of new portals for providing data access to different end-user communities; the scholarly publishing of datasets, and studies of the software development and testing processes used for the CMIP5 models.