Takeo Matsubara (松原武生, Takeo Matsubara, April 3, 1921 - December 15, 2014) was a Japanese physicist. Matsubara proposed a method of statistical mechanics related to Green's function (many-body theory), by applying quantum field theory techniques to statistical physics. This method, commonly known as Matsubara Green's function technique, introduces the notion of imaginary time, and the reciprocal variable to this imaginare time is known as discrete Matsubara frequency.