A quasilinear theory is formulated which includes the microscopic fluctuation fields as well as the coherent waves. The study emphasizes those cases in which the propagating mode of the fluctuation field gives rise to a dominant contribution to the particle correlation. In other words, in these cases the spontaneous Cˇerenkov emission of plasmons can play a more important role than the two‐particle collision process. The instability which is responsible for the turbulence can be of either an electrostatic, electromagnetic, or mixed nature. The effect of an external magnetic field is also considered in the present theory. The final result is valid for an arbitrary ratio of the energy density of the coherent wave to that of the fluctuation field althought the condition of weak turbulence is imposed throughout the analysis.