Almost all insulating solids, including natural minerals, glasses, and plastics, record tracks of nuclear charged particles. In this article, after first describing the nature of tracks in solids and ways of seeing them, we show how they have been used in such diverse problems as measuring the age of geological and archaeological specimens, studying the early history of the solar system recorded in meteorites, observing nuclear interactions, determining neutron fluxes, and separating biological cells of different sizes.