I would like to thank many colleagues for enlightening discussions on baryon spectroscopy during recent years: J.L. Ballot, S. Boukraa, M. Fabre de la Ripelle, D. Gromes, N. Isgur, G. Karl, D.B. Lichtenberg, E. Predazzi, J. Stubbe, A. Turbiner, and many others, with a special mention to my collaborators, who have elaborated most of the results presented here: J.–L. Basdevant, W.N. Cottingham, S. Fleck, C. Gignoux, H. Grosse, P. Hasenfratz, H. Høgaasen, R. Horgan, J. Kuti, A. Martin, B. Silvestre–Brac, P. Taxil, K. Tsu, and S. Zouzou. I have a deep gratitude to A. Martin for his advice on rigorous methods, to C. Gignoux for his decisive help on the Faddeev equations, to Sonia Fleck for her careful reading of the manuscript and many suggestions, and to Susan Leech O’Neale for her assistance in improving the english and the typography of the manuscript. Finally, I thank the members of the Theory Division at CERN, and, in particular J. Ellis, for their warm hospitality during the academic year 1990/91.