This paper contains a general discussion of electron drift in gases according to the method of free paths in which a fallacy contained in some earlier treatments is avoided. A general formula is derived for drift velocity in an electric field which is an arbitrary function of the time, and from it formulae for drift velocities in the following special cases of importance are deduced. drift in a constant electric field, in an alternating sinusoidal field, in a constant electric field with an applied magnetic field, in an alternating electric field with an applied magnetic field. Formulae for the electrical conductivity of an electron-laden gas follow from those for the drift velocities Applications of the formulae to ionospheric and other studies are mentioned.