Form factors and exclusive processes -- Introduction and Overview

Form factors, polarizabilities and excitation spectra are different aspects of many-body structures. These aspects are constrained by sum rules based on general principles like relativity, gauge invariance, causality and unitarity. Several such structure effects of baryons and mesons will be reviewed, with particular emphasis on the neutron charge form factor, the strangeness content of the nucleon, polarizabilities, and the Gerasimov-Drell-Hearn and related sum rules.