The recent advances in the toughening and reinforcing methods and theories in rigid inorganic particulate (RIP)-filled poly(propylene) (PP) composites have been reviewed. Studies have shown that under given conditions, in addition to the obvious increase of modulus, an obvious brittle-ductile transition also appears in these composites. The key to toughening a polymer is the role that inclusions can play as agents that (1) induce extensive plastic deformation following the interfacial debonding between the inclusion itself and the matrix, (2) induce shear yielding of the matrix, and (3) terminate the propagation of cracks. The main factors with regard to reinforcing mechanisms are how to enhance the interfacial bonding between the particles and the matrix and how to improve the dispersion of inclusions in the matrix. The major theories interpreting the toughening mechanisms of polymer-RIP composites include micro-voiding theory, damage competition theory, shear yielding theory, etc. It is necessary to form a soft shell/hard core structure to simultaneously toughen and reinforce polymers. Therefore, RIPS should be encapsulated with an elastic thin layer.