Hale's polarity law is an observational rule governing the direction of regions of strong magnetic fields on the Sun, which are grouped in pairs of opposite polarities. At any given time, the ordering of positive/negative regions with respect to the east-west direction (the direction of rotation) is the same in a given hemisphere, but is reversed from northern to southern hemispheres. This rule is named after George Hale who first established it. Shortly after his discovery, ongoing studies of the magnetic polarities of sunspot pairs by Hale and his collaborators revealed yet another intriguing pattern: from one sunspot cycle to the next, the magnetic polarities of sunspot pairs undergo a reversal in each hemisphere.