Quantum in-plane magnetoresistance in 2D electron systems

We review various aspects of magnetoresistance in (quasi-)twodimensional systems subject to an in-plane magnetic field. Concentrating on single-particle effects, three mechanisms leading to magnetoresistance are discussed: the orbital effect of the magnetic field -- due to inter-subband mixing -- and the sensitivity of this effect to the geometrical symmetry of the system, the interplay between spin-orbit coupling and Zeeman splitting, and the influence of the field on spin scattering at magnetic impurities.