A theory of solid-state fusion based on the formation of a D+ Bose Bloch condensate (BBC) is summarized. The first step toward fusion is a coalescence reaction that converts a multiple-occupation state of chemical density into a state of nuclear density. In PdDx, conditions for formation of a BBC are favorable when x is near unity, due to avoidance of lattice strain energy that otherwise contributes to the chemical potential. Fusion obeys a 3ldquo;boson in, boson out” selection rule and avoids the proton and neutron fluxes of collision-induced fusion. Some cold fusion studies are compatible with the theory and indicate the possibility of largely radiation-free commercial nuclear power from an inexhaustible fuel supply.