This paper presents a novel, unified approach to the theory of turbulent transport of parallel
momentum by collisionless drift waves. The physics of resonant and nonresonant off-
diagonal contributions to the momentum flux is emphasized, and collisionless momentum
exchange between waves and particles is accounted for. Two related momentum
conservation theorems are derived. These relate the resonant particle momentum flux, the
wave momentum flux, and the refractive force. A perturbative calculation, in the spirit of …