The authors present an analysis of the influence of various physics phenomena (which are not necessarily independent) on current drive performance in tokamaks. Such phenomena include diffraction and other non-geometrical optics processes, k|| modification, and multiple-pass absorption as well as antenna characteristics such as recessed cavity and septa geometry, poloidal extent and poloidal location of the current straps. The two-and-one-half-dimensional (21/2-D) full-wave code PICES is used for modelling ion cyclotron resonance heating and current drive. PICES is based on poloidal mode and reduced-order expansions. By 21/2-D, we mean that 3-D wave fields are calculated in axisymmetric geometry (2-D solution domain - ρ,θ), while the correct toroidal dependence of the antenna source currents is obtained from a 2-D (ρ ,phi) recessed antenna code. The calculation includes the poloidal and toroidal structure of the antenna, modification of the k|| spectrum due to the poloidal magnetic field and a complete solution for E||. A semi-analytic model for current drive, including trapped electron effects, is employed. These calculations are used extensively to model fast wave current drive in DIII-D, ITER and other tokamaks