One of the open challenges in subnuclear physics is to understand the
non-perturbative regime of Quantum Chromodynamics, including the world
of the nucleon and its excitations.
A necessary step towards this aim is a precise knowledge
of the experimental spectrum and the properties of baryon resonances.
Recently, large progress has been made based on photoproduction
experiments providing not only differential cross section
measurements but also high quality single and double polarization