Fundamentals of materials processes wherein a reinforcing phase is combined with bulk molten metal are reviewed. Capillary phenomena which govern the incorporation of the reinforcement into the matrix are discussed first, with focus on thermodynamics, mechanics, and chemistry of wetting. Engineering strategies that have been adopted to increase reinforcement wettability are also addressed. Relevant transport phenomena are covered next, with focus on the infiltration process and the rheology of composite slurries. The last section of this review is concerned with solidification of the matrix after it has been combined with the reinforcement, including nucleation and growth of the matrix, and particle pushing by the solidifying metal. This review places emphasis on the physical phenomena that govern the processing and the microstructural development of cast metal matrix composites.