Pulsar wind nebulae (PWNe) were the first objects where non-thermal polarized synchrotron emission was detected. They are one of the best astrophysical labs available for the study of high-energy processes like particle acceleration, properties of relativistic outflows, and non-thermal emission. Their broad-band spectrum makes them a suitable target for many instruments, and to date they are the only objects for which there is clear and undisputed evidence for high-energy X-ray polarized emission. In recent years a canonical model has been established which has proved incredibly successful in explaining many of the observed features. All of this makes PWNe a prime candidate for any future X-ray polarimetry study. I will review here the current MHD model, what we know from polarization in the optical and radio band, and what we might learn from next-generation polarimetry.