Two nonlinear propagation effects which limit the transmission of intense laser radiation through the atmosphere are discussed, namely, self-defocusing due to atmospheric heating, and the stimulated Raman effect. The self-defocusing studies are restricted, in this report, to the heating mechanisms, and in particular to the theory of the very far wings of atmospheric absorption lines, beyond the domain of conventional pressure broadening theories. Specifically, in order to understand the apparent dominance of H2O absorptivity in the atmosphere at the 10 microns window, the very far wing collision broadening of the rotational spectrum of polar molecules is investigated. First, the classical Debye theory of dielectric absorptivity is extended to account for higher frequencies and finite collisional time duration. It is then demonstrated that this theory is inadequate to explain the dominant role of H2O - H2O collisions observed in recent experiments at 10 microns with H2O - N2 mixtures, and it is found necessary to introduce a new mechanism: a hindered rotation, or librational motion, arising from the angular dependence of the strong dipole-dipole interaction. Preliminary calculations indicate that this mechanism is promising. With regard to the Raman effect, a previously developed theory of stimulated Raman propagation is applied to describe a Raman amplifier and also to explain recent observations of very short intense pulses of Raman backscattered light. (Author).