Physics of nonhermitian degeneracies

A summary, with references and additional comments, of a talk delivered at the Second International Workshop on Pseudohermitian Hamiltonians in Quantum Physics (Prague, 14-16 June 2004). After explaining some general features of nonhermitian degeneracies ('exceptional points'), several applications are outlined: to multiple reflections in a pile of plates, linewidths of unstable lasers, atom diffraction by light, and crystal optics.