Cs 2 [Au I X 2 ][Au I I I X 4 ] (X = Cl,Br,I) are three-dimensional halogen-bridged Au mixed-valence compounds having perovskite type structure. These compounds undergo the pressure induced Au valence transition from the Au I , I I I mixed-valence state to the homogeneous Au I I state, which is coupled with a structural phase transition. In the pressure region below the Au valence transition, these compounds show a metallic behavior, which is attributed to a dynamic two-electron exchange between Au I and Au I I I (i.e. highly mobile bipolarons). In the case of Cs 2 Au 2 I 6 the electrical resistivity as a function of temperature shows a re-entrant phenomenon of the metallic bipolaron phase in the vicinity of the Au valence transition.