We generalize Harish-Chandra-Itzykson-Zuber and certain other integrals (Gross-Witten integral and integrals over complex matrices) using the notion of tau function of matrix argument. In this case one can reduce matrix integral to the integral over eigenvalues, which in turn is certain tau function. Soliton theory. KP hierarchy of integrable equations, which is the most popular example, consis...