Mechanical flotation of gangue minerals is reviewed. First, mechanisms that contribute to gangue transportation are considered. The effect of water recovery and other essential factors on gangue recovery is described, and mathematical models for classification and entrainment of gangue are presented. The importance of froth characteristics is also discussed. An analysis method to evaluate the entrainment of gangue in flotation circuits is presented. Measures to restrain the mechanical flotation of gangue are also considered.