Common properties of photometric systems. Energy distribution in stellar spectra. Interstellar extinction. Atmospheric extinction. Broad-band photometric systems introduced before 1953. The UBV system. Broad bandpass systems containing infrared. The uvby+beta system. Other medium- and narrow-band photometric systems. The Vilnius photometric system. Appendices: absolute magnitudes, effective temperatures, bolometric corrections, surface gravities, masses and radii of stars.