Results of experimental studies of the X-pinch since its invention and implementation in 1982 at the Lebedev Physical Institute are presented. The review consists of two parts. The first part briefly outlines the history of creation and studies of X-pinches, describes the diagnostic techniques and devices developed during these studies, and presents the main results obtained in studying the physical processes occurring in the X-pinch. The second part is devoted to the results of detailed studies of the spatial, temporal, and spectral characteristics of the X-pinch hot spot—the region where the highest plasma parameters are achieved and which is a source of X-ray emission with extreme parameters. Some results of X-pinch simulations are also presented.