The proceedings of IAU S317 offer an updated view of the stellar halos of galaxies, from the local universe to more distant systems, discussing differences and similarities among them. They review the results of ongoing large photometric and spectroscopic surveys and compare them to the predictions of new generation simulations at the forefront of our technical capabilities. Structures are analysed on both large and small scales, with attention given to the kinematical and chemical properties of their smallest and oldest components. A number of excellent reviews on state-of-the-art research, covering fields such as first stars, galactic archaeology, stellar halos in cosmological simulations, discrete constituents of stellar halos - from field, isolated stars to globular clusters and planetary nebulae - are accompanied by contributed papers presenting the results of original research by top-level specialists in the area. IAU S317 benefits researchers with interests encompassing stellar and galactic astrophysics and galaxy evolution.

Stellar cluster research is in a dynamic state. IAU Symposium 351 (also chosen as MODEST-19, within the 'Modelling and Observing DEnse STellar systems' meeting series) is a compilation of the research presented at the Symposium. It contains highlights of the latest research taking place in many areas, including the formation of stellar clusters at high redshifts, multiple stellar populations within stellar clusters, the dynamical evolution of stellar clusters, and the production of exotic objects such as black holes within stellar clusters. This volume also includes articles on the build up of larger galaxies from smaller galaxies and stellar clusters, and discussions of the latest data from large surveys and from the Gaia satellite. Looking at both the local and the high-redshift universe allows links to be established between the clusters we see today and their progenitors. IAU S351 is an ideal entry point for astronomers new to this research field.