Quark and lepton masses

Abstract

Quarks and leptons, the fundamental building blocks of the subatomic world, manifest in three families - replicas with identical quantum numbers that differ only in their masses. After summarizing the present data, an overview is presented of the main attempts to explain the origin of the observed patterns and trace it back to an as-yet-unknown fundamental principle.

Invited chapter for the Encyclopedia of Particle Physics, 27 pages, 12 figures,