This publication provides background in terms of requirements and recommendations for a functional and robust Global Climate Observing System (GCOS). Global climate monitoring, including water and greenhouse-gas fluxes, supports and serves the programmes of WMO and its Member States, especially with a view towards the United Nations Sustainable Development Goals (SDGs) and implementation of the Paris Agreement. While observations are the focus of National Meteorological and Hydrological Services (NMHSs), aspects of climate-related policy are covered by many different government departments. All these will benefit from the information on implementation needs described herein, provided by GCOS.