Known as well as β CMa stars, the classical β Cep stars are a group of variables of spectral type between BO to B2 and luminosity classes II to IV with light and radial velocity periods between 3 and 7 hours and radial velocity ranges usually < 50 km/sec. Their photometric amplitudes are usually < 0.1 mag in the visible. The light curves are approximately sinusoidal (however, multiple modes are frequently detected with low amplitudes), which lag about 90° behind the radial velocity curve and the color changes in the blue and visual spectral regions are small. Color and luminosity show that maximum temperature coincides with minimum radius. Probably not all the stars in this spectral range are variables; most investigators searching in this region for β Cep variables have observed that a large number of stars in this zone are constant in light. Also, the β Cep stars are not different spectroscopically from nonvariable stars of the same MK type.