Claudio Pellegrini (born in Rome on May 9, 1935) is an Italian/American physicist known for his pioneering work on X-ray free electron lasers and collective effects in relativistic particle beams. He was educated at the Sapienza University of Rome where he received the Laurea in Fisica summa cum laude in 1958 and the Libera Docenza, in 1965. From 1958 to 1978, he worked at the Laboratori Nazionali di Frascati for high energy and nuclear physics. In the early 1960s, he was at the Nordic Institute for Theoretical Physics (NORDITA) in Copenhagen, working on an alternative formulation of the theory of general relativity using tetrad fields to obtain, among other things, a better description of the energy-momentum complex. (See Teleparallelism for a summary of the theoretical context of this wo