Wolf-Rayet stars from the past to the present

After a short report on the discovery in 1867, by Charles Wolf and Georges Rayet, of a peculiar type of emission line stars in Cygnus, the classification scheme applied to population I Wolf-Rayet stars is described, followed by a review of the basic physical parameters of these starts: luminosity, temperature, mass and chemical composition. The statistical properties that result from the census of the Wolf-Rayet populations in our Galaxy, the Magellanic Clouds and a few nearby galaxies are analysed. Finally the fundamental issue of the origin and evolution of Wolf-Rayet starts is addressed. Mass loss by stellar winds in massive stars is recognized as being probably the most efficient mechanism to form Wolf-Rayet stars.