Amongst the most stringent limitations in astronomy and cosmology are the very large uncertainties on galaxy masses and sizes. Yet, this topic is undergoing a revolution due to increasing knowledge of 6D space-velocity data for galaxies in the Local Group. This is driven by Gaia and numerous accompanying surveys that provide an accurate Milky Way rotation curve, detailed orbits of the nearby dwarf galaxies, and first estimates of the motions of dwarf irregulars and in the M31 system. This IAU Symposium has a very focused goal: Determining the mass of galaxies from dwarfs to giant spirals. However, it addresses a very broad range of astronomical fields (from studies of variable stars for estimating distances to dynamical modeling), of wave-lengths to be investigated (from radio and optical for estimating the HI gas and stellar content and their motions, to X-rays for estimating the warm and hot ionized gas), and has major implications for a fundamental question (from the distribution and nature of dark matter to alternative models). Measuring galaxy masses at different scales in the Local Group impacts a broad range of astronomy, from stars, star clusters, to the Milky Way, distant galaxies, and Cosmology.
Telegrafenberg, Potsdam, Germany