The theory and measurement of the electromagnetic correlation between orthogonal linearly polarized returns In two-channel precipitation radars is summarized. The relationship of the properties of precipitation particles to the cross-correlation as a function of polarization direction is discussed. Also considered is the relationship of correlation in a linearly polarized radar system to the corresponding circular polarisation characteristics. The formulation for the cross-correlation at linear polarization is extended to Include coverage of more general models of the distribution function for precipitation particle canting angle. Typical experimental results showing measured values of cross-correlation with rotating linear polarization are presented.