Electro- and photoproduction of meson and baryon resonances

I discuss the physics of quantum mechanical resonances, and the phenomenology of their excitation and observation in the absorption of photons on nucleons. I begin with a discussion of resonance phenomena in classical physics, in quantum mechanics, and finally incorporating relativistic effects. As an example, I consider in detail J(PC) = 1(--) states produced in the reaction e(+)e(-) --> gamma (star)--> pi (+)pi (-). Next, the phenomenology of meson and baryon resonances are discussed in the context of the quark model. Finally, I discuss baryon resonances and their partial wave analysis in pi (+/-)p --> piN reactions, and then in the more complicated, but still straightforward, case of gammap --> piN. I conclude with a topical discussion of current research areas, including electroproduction of baryon resonances, and of quasi-twobody photoproduction processes, and the isobar model partial wave analysis, in the reaction gammap --> p pi (+)pi (-).