Micro-Doppler signatures have been widely applied in civilian and military uses, In the paper, an overview of recent advances in extractions and applications of radar micro-Doppler signatures is presented, including recognition of space, air, and ground targets, combined micro-Doppler with range-Doppler features, through-wall micro-Doppler signatures, multistatic micro-Doppler signatures, decomposition of micro-Doppler signatures, and detection and extraction of micro motions in human body, such as heart beats and respirations.