Mass is one of the most fundamental quantities that characterise stellar systems, from star clusters to large galaxies. It determines both the internal dynamics of the system and its gravitational interaction with other systems. For the galaxies in the Local Group, a real revolution in the topic has occurred with the Gaia satellite that provides six-dimensional data (three-dimensional positions and velocities) for almost 1.5 billion sources, located both in the Milky Way and in Local Group galaxies. IAU Symposium 379 gathered together the community working on this topic to discuss and collect recent advances and provide an opportunity for researchers to meet, exchange ideas, and compare methods and hypothesis. Measuring galaxy masses at different scales in the Local Group impacts a broad range of astronomy, from stars and star clusters, to the Milky Way, distant galaxies, and cosmology.
