New ground-based BVRI CCD observations of the eclipsing binary system BY Peg are presented. New times of minima are given and a new ephemeris is proposed. The light curves are analyzed using the Wilson-Devinney light curve synthesis code and new geometric and photometric elements are derived. Empirical laws, such as M-R and M-L diagrams and those derived from the correlation between physical parameters of contact binaries, are used in order to compare the physical parameters of the system with their theoretical (expected) values. The system BY Peg is found to be an evolved W-type W UMa system, showing total eclipses.