Luminosity is a key parameter that quantifies the performance of a particle collider. Yet, the precise measurement of luminosity at hadron colliders is especially challenging. The van der Meer method for the calibration of absolute luminosity will be described. Various detector technologies which are used for luminosity measurement will be discussed. The currently-operational CMS luminometers will be highlighted and plans for future luminosity measurement at CMS will be outlined. Finally, the operational experience of the Pixel Luminosity Telescope will be summarized -- from a single-crystal diamond sensor prototype, to an actively-cooled silicon sensor Run-2 detector, to its rebuild during the LHC's Long Shutdown 2, to its commissioning and performance during Run-3.