Leonidas "Leo" K. Resvanis (Greek: Λεωνίδας Ρεσβάνης; 1944 in Athens, Greece) is a physicist known for his work with neutrinos. He is a Professor of Physics at the University of Athens and the director of the Nestor Project.
He is also the person who suggested to Burton Richter that Richter's new discovery be named the "psi" particle.
Leonidas Resvanis received his B.Sc. in Physics from the University of Manchester in 1965. He continue his studies in the Johns Hopkins University from where he received his PhD in High Energy Physics in 1971.
Between 1971 and 1976 he worked in the United States, in the University of Pennsylvania as an assistant professor. In 1976 was elected a full Professor in the University of Athens.