The structures and phase transitions of N2O were studied by powder x‐ray diffraction in a tungsten–carbide anvil device from about 100 to 300 K and 2 to 12 GPa. Two solid phases, α‐N2O and β‐N2O, were observed. The α pattern is consistent with the known low‐pressure low‐temperature ordered cubic form, space group Pa3, up to 4.8 GPa where transition to a new β solid occurs. From refinements using photographic x‐ray intensities, the β‐N2O structure was determined to be orthorhombic Cmca. There are four molecules in a unit cell with a=4.954 Å, b=4.497 Å, and c=6.201 Å at 5.81 GPa and 298 K. The molecular axes lie parallel to the b c plane and are tipped at an angle of 37.2° to the b axis. Random head‐to‐tail orientation is probable in both solids. The phase diagram and values of the molar volume for N2O are compared with published data for the isoelectronic molecule CO2. Recent theoretical calculations correctly predict the β‐N2O structure.