SPARC (Stratosphere–troposphere Processes And their Role in Climate), is one of the core projects of the World Climate Research Programme (WCRP). S-RIP was a coordinated activity, which started in 2013, to compare global atmospheric reanalysis data sets using a variety of key diagnostics. The objectives of this project were to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The studies in S-RIP are to be published in several journal papers and the WCRP/SPARC reports.