  The electromagnetic excitation of the nucleon resonances is studied in the
framework of Constituent Quark Models. Particular attention is devoted to the
transition to the $\Delta$ resonance and to the issue of a possible deformation
of hadronic systems, mainly in connection with the problem of the quadrupole
excitation. The analysis of the emerging discrepancies between data and
theoretical predictions is discussed and shown to lead to important conclusions
concerning the internal dynamical structure of hadrons.
