On basis of the results of the previous researches on composite foundations, the authors present the basic concepts, types and features of composite foundations. The authors also present the principles, forms and mechanisms of CM threedimension composite foundations. In composite foundations, Mpiles are used to strengthen the soft subsoil, Cpiles are used to control the settlement and cushions are used to modify and improve the shares of the stress taken by the piles and subsoil. The authors also provide the design and calculation procedures for the bearing capacity and settlement of CM threedimension composite foundations.