The effects of both absorption and dispersion in the earth's atmosphere on the propagation of very short pulses in the microwave and millimetre-wavelength regions of the electromagnetic spectrum are calculated for line-of-sight transmissions and for earth–space paths. For pulses as short as 0.1 ns, the effects are found to be severe, both in terms of pulse distortion, in the form of either the broadening or the compression of the pulse, and in terms of a shift in the frequency at which maximum energy in the pulse is received. Pulse compression is found to occur in those regions of the electromagnetic spectrum where the second derivative of the absorption coefficient is negative.