In this study, quasi-static crack initiation under mixed mode loading in planar (2-D) functionally graded materials is presented. First, crack initiation in the homogeneous material which forms the basis of our FGM - polyethylene - is studied. The Generalized Maximum Tangential Stress Criterion (GMTS) is applied through use of finite elements to determine crack initiation angles in a cracked 2-D functionally graded material. The effects of crack length, T-stress, inherent length scale r(c) and mode mixity are discussed. Computational results of crack initiation angles are compared to experimental results obtained using functionally graded polyethylene. Stress Intensity factors for a center cracked FGM are calculated.