On the basis of the experimental data and physical principles, we formulate the principal conditions of getting stable solid-phase joints of dissimilar materials as a result of their simultaneous vacuum hot rolling, namely, the possibility of sliding of one metal over the other, the motion of metals must obey the Bernoulli equation for incompressible liquids, the possibility of mass transfer of the atoms of dissimilar metals through their common boundary, the continuity of the flow or the second-by-second equality of the masses of rolled metal, and the equality of powers acquired by the metals.