Interlinking observation systems requires common standards for architecture and data sharing. The architecture of an Earth observation system refers to the way in which its components are designed so that they function as a whole. Each GEOSS component must be included in the GEOSS registry and configured so that it can communicate with the other participating systems. In addition, each contributor to GEOSS must subscribe to the GEO data-sharing principles, which aim to ensure the full and open exchange of data, metadata and products. These issues are fundamental to the successful operation of GEOSS.