Whether or not a particle is captured by a rising bubble during flotation is determined, to a large degree, by the hydrophobic force of attraction. The origins of the latter force have remained obscure, despite the early insights of flotation scientists. Recent evidence indicates that the surface properties of the solid substrate, the type and concentration of dissolved gas, and surface microbubbles all influence the stability of the thin, aqueous film that forms between a particle and a gas bubble during the final stages of the capture process. The accurate description of the forces that operate across this film remains a serious challenge.