Polymer electrets have been widely explored as charge-storage elements in field-effect transistor memory and artificial synaptic devices because of their tailorable molecular structures and processability. Proper design of polymer electrets can enhance the charge injection efficiency and storage time, and the memory implementation can be switched from electrical to optical programming. We comprehensively review state-of-the-art polymer electrets for transistor-structured memory and artificial synapses. We classify the electrets into five types: (1) pendant polymer electrets, (2) block copolymer electrets, (3) conjugated polymer electrets, (4) hybrid polymer composites, and (5) ferroelectric polymer electrets. Their design concepts and working mechanisms are discussed in detail. This review may pave the way for the development of polymer-electret-based transistor memory devices and artificial synapses with unprecedented performance improvements.