Constantino Tsallis (/ˈsælɪs/; Greek: Κωνσταντίνος Τσάλλης [ˈtsalis]; born 4 November 1943) is a naturalized Brazilian physicist of Greek descent, working in Rio de Janeiro at Centro Brasileiro de Pesquisas Físicas (CBPF), Brazil.

Tsallis was born in Greece, and grew up in Argentina, where he studied physics at Instituto Balseiro, in Bariloche.

In 1974, he received a Doctorat d'État ès Sciences Physiques degree from the University of Paris-Sud.

The resulting theory is not intended to replace Boltzmann–Gibbs statistics, but rather supplement it, such as in the case of anomalous systems characterised by non-ergodicity or metastable states.

One experimental verification of the predictions of Tsallis statistics concerned cold atoms in dissipative optical lattices.