Hadron spectra and quarks

The quark model began as little more than a quantum-number counting device. After a brief period during which quarks only played a symmetry role, serious interest in quark dynamics developed. The marriage of the principle of local gauge invariance and quarks has been astonishingly productive. Although many questions still need to be be answered, there is little doubt that the strong, weak and electroweak interactions of matter are described by gauge theories of interactions of the quarks. This review is focussed on the successes