CLIO (Centre Laser Infrarouge d’Orsay) is a pulsed free-electron laser user facility producing a high peak power and continously tunable wavelength laser beam in the mid-infrared spectral range between 3 and 120 µm. It has a double pulsed structure: "macro-pulses" 10 µs long (at 1 to 25 Hz) contain "micro-pulses", of length adjustable from 0.3 to 5 ps (with Fourier transform spectral width). The micropulse interval is 16 ns. A purged beam line transports the optical beam to eight user rooms. They include various equipment : mirrors, detectors, optical mounts, monochromators, cryostats, etc. Users have computer control of the laser wavelength and spectral scans. In addition, four different set-ups are operated by permanent scientists and are open users : surface spectroscopy; ultrasensitive molecular spectroscopy (2); near-field microspectroscopy.CLIO is open to the scientific community. Proposals are selected on the basis of scientific merit through an independent peer-review process. The use of CLIO is free of charge for the academic community. The projects have to be submitted by the end of each year.