Since circular polarimetric radars can be used to assess the relative contribution of odd-bounce and even-bounce scattering to the response of targets and to implement novel schemes for adaptive rain clutter suppression and radar pulse compression, they are increasingly used in applications such as radar meteorology, biophysical and geophysical remote sensing, and radar navigation. Although methods for calibrating linear polarimetric radars are widely known, they cannot be used to calibrate circular polarimetric radars until account is taken for the different form of the response of calibration targets when measured with respect to a circularly polarized basis. The response of three standard targets used to calibrate linear polarimetric radars (an odd-bounce-reflector and two even-bounce reflectors with different angles of rotation about the radar line-of-sight) does not yield a unique solution to the calibration equations. If, however, the odd-bounce reflector is replaced by either a circularly polarizing or linear polarization selective target, the calibration equations can be solved.