We present numerical simulations of interacting drops and bubbles. In particular, we give an overview of the partial coalescence of drops with a reservoir or larger drop. After presenting the basic mechanism at play, as confirmed by numerical simulations and experimental evidence, we investigate cases where the surface tension of the drop differs from that of the reservoir because of compositional differences. We also present numerical simulations of partial or total coalescence in the presence of surfactants. Time permitting, we will describe how the settling of drops in a stratified ambient is affected by density and surface tension variations, even when the latter are very small.