This special issue was initiated by the Indian Ocean Region Panel and coincides with the launch of the second International Indian Ocean Expedition (IIOE2) at the International Symposium on the Indian Ocean (IO50) that will be held on 30 November - 4 December 2015 at the National Institute of Oceanography (NIO), Goa, India. We thank our Guest Editors - Jérôme Vialard (co-Chair of CLIVAR/IOC-GOOS Indian Ocean Region Panel), Satheesh Shenoi (Director of INCOIS, India), Wajih Naqvi (Director of NIO, India) and Raleigh Hood (Chair of the IIOE2 Planning Committee) - and the contributing authors for compiling an excellent collection of articles that report on recent scientific results, key topics for future research, and ongoing and future process studies and research projects.  Articles describe the legacy of IIOE and the next phase, IIOE2, and highlight the global climatic relevance of the Indian Ocean.