Metallic foams offer significant performance gains in light, stiff structures due to their excellent stiffness to density ratios. Potential applications are lightweight structures and biomedical implants as well as numerous other industrial applications and even futuristic floating mega structures. A valid constitutive model, which is able to represent the response of porous metal under multiaxial loading, is essential for practical mechanical design. While the elastic response has closed-form solutions, the inelastic behavior is more complicated as it requires a stress-strain history in addition to an adjusted reduced initial yield caused by the degradation of the material. The diversity of pores shapes and sizes further complicate the task of devising a single valid constitutive model. Metallic foams plastic constitutive law, in contrast to dense metals, is both compressible and pressure dependent. The methods reviewed in this thesis, namely Gurson's void growth model (1975) and the more recent constitutive model devised by Deshpande & Fleck (2000),each propose a way of incorporating those effects, either analytically or empirically. This study strives to achieve engineering insight and guidelines as to where and when to employ each method/model, by interpretation of similarities and differences found from comparisons. The well established micromechanical method 'High fidelity method of cells', HFGMC, devised by Aboudi (2003) is used as a basis of comparison. For low porosities (<20%) both the Deshpande & Fleck model and Gurson's model show close resemblance with the HFGMC predictions. For higher porosities the models deviate severely. Due to recent developments in the production of this type of materials, it is expected that the recent study would be useful to researches