A large number of engineering alloys consist of two ductile phases; for example alpha/beta titanium alloys, alpha/beta brasses and dual phase steels. Whenever a material consisting of two or more component phases with different properties is subjected to stress, in general, the phases deform differently. This results in additional interaction stresses and strains and their magnitude depends on such factors as the property difference between phases, and morphology and volume fraction of phases. Due to these complexities, the properties of two-phase materials, in general, cannot be predicted on the basis of simple laws such as the law of mixtures. The aim of this review paper is to describe how the various parameters such as morphology and volume percent of phases affect the mechanical properties of two-phase materials. Such information will be of great use in designing and selecting two-phase materials for various engineering applications. (c) 2005 Elsevier Ltd. All rights reserved.