A first Marine Ecosystem Assessment for the Southern Ocean (MEASO) is under development. MEASO aims to provide a forward-looking assessment of what trends in Southern Ocean ecosystems are happening now and into the future, and what may need to be planned for, in terms of research and management. The aim is to have a quantitative assessment that enables managers to achieve consensus in adapting their management strategies to ecosystem change. MEASO officially began at an international conference held in Hobart in early April 2018 (http://www.measo2018.aq/). The conference provided an opportunity to share relevant science, enhance community input into the design and planning of the MEASO, and to develop a work plan. Since the conference, summaries of information available for a MEASO have been compiled in order to determine what can be used to assess status and trends within the Southern Ocean on regional and circumpolar scales. This review includes a record of field programmes and ecological surveys, current Southern Ocean syntheses, model coverage and assessments. The types of biological data collected from the field programmes are also being summarised, based on an open, international survey of researchers. For this survey, an indication of where and when national research programmes have conducted field work were requested, particularly for measures of density (abundance) for different taxonomic and functional groups within the benthos, pelagos and plankton as well as birds and marine mammals. To date 12 countries have contributed to the data survey, coverage of which can be viewed on the Southern Ocean Knowledge and Information wiki: http://soki.aq/display/MEASO/MEASO+Data+Availability. The work program for the first assessment is detailed in the paper.