The Adaptable Input/Output (I/O) System, ADIOS 2 is developed as part of the United States Department of Energy's Exascale Computing Program. ADIOS 2 is a framework designed for scientific data I/O to publish and subscribe (put/get) data when and where required. ADIOS 2 transports data as groups of self-describing variables and attributes across different media types (such as files, wide-area-networks, and remote direct memory access) using a common application programming interface for all transport modes. ADIOS 2 can be used on supercomputers, commercial clouds, and personal computers. ADIOS 2 focuses on: * Performance I/O scalability in high performance computing (HPC) applications. * Adaptability unified interfaces to allow for several modes of transport (files, memory-to-memory) * Ease of Use two-level application programming interface (APIs) * Full APIs for HPC applications: C++11, Fortran 90, C 99, Python 2 and 3 * Simplified High-Level APIs for data analysis: Python 2 and 3, C++11, Matlab