The existence of a novel double-molybdate phase with a palmierite-type structure, Cs2Ba(MoO4)(2), is revealed in this work, and its structural properties at room temperature have been characterized in detail using X-ray and neutron diffraction measurements. In addition, its thermal stability and thermal expansion are investigated in the temperature range 298673 K using high-temperature X-ray diffraction, leading to the volumetric thermal expansion coefficient a a(V) >> 43.0 x 106 K-1. The compounds standard enthalpy of formation at 298.15 K has been obtained using solution calorimetry, which yielded D(f)Hm degrees(Cs2Ba(MoO4)(2), cr, 298.15 K) = -3066.6 +/- 3.1 kJ. mol(1), and its standard entropy at 298.15 K has been derived from low-temperature (2.1294.3 K) thermal-relaxation calorimetry as S degrees(Cs2Ba(MoO4)(2), cr, 298.15 K) = 381.2 +/- 11.8 J K-1 mol(1).