An optical system for rapid routine pressure measurement is described which utilizes a pressure shift in the sharp R‐line fluorescence spectrum of ruby or similar materials. The system, which consists of a standard polarizing microscope and a 1/4 m monochromator with associated photodetection system, is used with the diamond‐anvil pressure cell, but can be employed with suitable modification in any pressure system which has optical access. The precision of the pressure measurement in a hydrostatic environment up to 100 kilobar is 0.5 kilobar using ruby as the pressure sensor. This precision is better than the accuracy of the present pressure scale above 40 kilobar. The merits of fluorescent materials other than ruby as pressure sensors are also discussed. A description of a Waspaloy diamond cell with some modifications in design is given. This improved cell and associated techniques extends the pressure range in gasketed systems up to 200 kilobar at room temperature and to moderate pressures at 700° C.