The accretion and differentiation of planetary bodies set the initial conditions for the evolution of their cores, mantles, and atmospheres. Understanding of planetary accretion and differentiation requires detailed studies of a complex series of processes over a wide range of time and spatial scales, beginning with the aggregation of gas and dust in the proto-solar disk, continuing through impacts and collisions between planetesimals, culminating in magmatic differentiation. This interdisciplinary session invites contributions that utilize lab experiments, chemical analyses of planetary materials, numerical modeling, and remote observations to study various aspects and stages of planetary formation, including but not limited to, collisional growth of planetesimals, planetary embryo and satellite formation, core-mantle-atmosphere differentiation, magma oceans, and delivery and loss of volatile elements.