The free-electron has proven to be an invaluable source of radiation in the infrared spectral range. Its main qualities are its spectral range (from near-IR to mm waves), its tuning range (at least a decade for a given FEL) and tuning speeds (minutes), its high peak power (hundreds of MW) and its the short pulse lengths (down to 200 fs). In the last decade, several FELs have been designed and built as user dedicated facilities. Presently, 7 infrared FELs are running more than 1000 hours/year for users, who are working in various scientific fields.