After a short period at CERN, Ginevra he returned to Italy and started research on lasers, light-matter interactions, nonlinear optics, etc. He is the author of about 500 papers on peer reviewed physics journals. He is fellow of IOP, American Optical Society, Italian Physical Society, Italian Optical and Photonic Society of which he has been the president, European Optical Society in which he held and is holding several positions. He is member of European Physical Society, where he held positions several years ago. Mario Bertolotti has been member of scientific committee in several journals. He was editor of the journal Pure and Applied Optics edited by IOP, he is editor of the Journal of the European Optical Society: Rapid Publications (JEOS:RP), an electronic journal. He has been director of several summer schools in Erice, and other places.
He was also interested in the hystoric developments of physics and wrote two books on the history of lasers.Cosmic rays were a subject of his interest altough he never worked actively in the field.