Isaak Markovich Khalatnikov (Russian: Исаак Маркович Халатников; born 17 October 1919) is a leading Soviet physicist, well known for his role in developing the BKL conjecture in general relativity.

Khalatnikov was born in Dnipropetrovsk and graduated from Dnipropetrovsk State University with a degree in Physics in 1941. He is a member of the Communist Party since 1944. He earned his doctorate in 1952. His wife Valentina was the daughter of Revolutionary hero Nikolay Shchors.

Much of Khalatnikov's research has been a collaboration with, or inspired by, Lev Landau, including the Landau-Khalatnikov theory of superfluidity.

In 1970, inspired by the mixmaster model introduced by Charles W. Misner, then at Princeton University, Khalatnikov, together with Vladimir A. Belinsky and Evgeny Mikhailovich Lifshitz, introduced what has become known as the BKL conjecture, which is widely regarded as one of the most outstanding open problems in the classical theory of gravitation.

Khalatnikov directed the Landau Institute for Theoretical Physics in Moscow from 1965 to 1992. He was elected to the Soviet Academy of Sciences in 1984. He has been awarded the Landau Prize and the Alexander von Humboldt Award, and is a foreign member of the Royal Society of London.