A general model is presented for predicting entrainment conditions for nonuniform, noncohesive sediments. The model is based on an analysis of the moments of forces acting on a particle at the condition of incipient motion. Particle geometry and packing arrangement are accounted for as well as variations of near bed flow velocity and drag and lift coefficients for a wide range of flow conditions. Model predictions agree well with laboratory and field measurements for uniform sediments and for protrusion and relative size effects.