A theory is developed for the ambipolar diffusion, drift, distortion, and production of ionization irregularities within weakly ionized plasma in the presence of the geomagnetic field and motions of the neutral gas. The formulation takes into consideration turbulent, wave, or uniform motion of the neutral gas, as well as the effects of uniform electric and gravitational fields. Equations are developed for a multispecies plasma containing ions of either sign of electric charge; later these equations are specialized to the case of electrons and one species of positive ions. New effects are found relating to the production of ionization irregularities by the coupling of the geomagnetic field with the spatial variation of the velocity field and acceleration field of the neutral gas. The quasineutral approximation and linearization are used to produce a more tractable theory. The lengthscale restrictions necessary for the ionosphere to be treated as a homogeneous plasma are considered. The drift and distortion of ionization irregularities because of the gravitational field, a uniform wind and electric field are considered for the lower ionosphere, as is ambipolar diffusion. The production of ionization irregularities by wind shear an by the convergence of the neutral gas along a magnetic field line and divergence perpendicular to it are investigated, and the fluctuations in electron concentration so produced are estimated.