The laboratory photolysis of chlorine nitrate (ClONO2) with 302.5 nm ultraviolet light leads to the destruction per quantum of 4 molecules of ClONO2 and the formation of 1 molecule of O2, 2 of Cl2 and 2 of N2O5. These quantum yields are not consistent with the current assumption that the primary photolysis step for ClONO2 in the stratosphere leads to the formation of ClO plus NO2. A consistent mechanism exists in which the photolytic step involves the decomposition of ClONO2 to ClONO+O(3P). The onset of observed absorption of radiation by ClONO2 corresponds approximately to the thermodynamic accessibility of this simple splitting away of an O atom. The photolysis of ClONO occurs very rapidly in the stratosphere, either to Cl+NO2 or ClO+NO. The substitution of either Cl+NO2+O or ClO+NO+O for ClO+NO2 as the eventual photolysis products from ClONO2 is not expected to cause appreciable alteration in predictions from stratospheric modeling. ¿ 1977 American Geophysical Union