Mass loss from evolved massive stars is a major contributor to the chemical enrichment of the interstellar medium, the Galaxy, and ultimately the Universe. To assemble a clear view of their cosmic impact, it is essential to understand their physics, from the photosphere to the interstellar medium. The violent convective motions, low surface gravity, and high luminosity combine to trigger an intense stellar wind, complex chemistry and dust formation. Thanks to its proximity and brightness, Betelgeuse is a particularly important fiducial star to study in details the physical phenomena at play in red supergiants. Impressive progress has been made recently on our understanding of Betelgeuse and other evolved massive stars, thanks to new observations from ESO's VLT, Herschel, NRAO's VLA and other facilities. Considerable advances also came from theory and numerical simulations. The goal of the Betelgeuse workshop was to present a coherent panorama of these results, and discuss possible future research axes in this field. The proceedings reflect these discussions, and therefore cover a broad range of topics, from numerical simulations to observations. They are directed towards researchers and graduate students.