In recent years, P/M techniques have been combined with conventional deformation processes to manufacture various engineering products. During the forging of a metal powder preform, changes in volume and density occur, and the various theoretical analyses developed based on volume constancy cannot be applied to the deformation of porous materials. The paper reviews some of the work carried out in chronological order. A mathematical solution was developed for axisymmetric forging of iron powder preforms (solid and hollow) under the frictional conditions based on the yield criteria proposed by Tabata and Masaki for porous materials. The theoretical values agreed with experimental values within accuracy (85-95%).