By its very nature, meteorology is global and transboundary in scope. The World Meteorological Organisation (WMO) exists, therefore, essentially to facilitate the international coordination, standardisation and maintenance of meteorological observing, data exchange and data-processing facilities, directed ultimately at the provision of meteorological data and services for the benefit of mankind. It does this, inter alia, through providing assistance, as required, in the development of national facilities and human resources to allow every national Meteorological Service to both participate in and benefit from the global systems and programmes. National Meteorological Services have traditionally been concerned with the collection of meteorological and oceanographic data at sea and with the provision of meteorological and related services for the mariner. This involvement has expanded rapidly over the past two decades with expanding utilisation of the oceans and concern for the sustainable management of the marine environment, as well as an increasing realisation of the critical role of the oceans in the global climate system. WMO's efforts to strengthen national Meteorological Services have therefore included an important element of marine capacity building. This paper gives an overview of WMO's technical cooperation and education and training activities in general, before outlining in more detail the requirements for and activities of the Organisation in marine capacity building. These activities are illustrated through three specific case studies, giving three different types of assistance and three different degrees of success. The paper concludes by analysing the reasons for success or failure and drawing lessons from these for the future directions of our work in marine capacity building.