Abstract. Organic peroxy radicals (RO₂), formed from the degradation of hydrocarbons and other volatile organic compounds (VOCs), play a key role in tropospheric oxidation mechanisms. Several competing reactions may be available for a given RO₂ radical, the relative rates of which depend on both the structure of RO₂ and the ambient conditions. Published kinetics and branching ratio data are reviewed for the bimolecular reactions of RO₂ with NO, NO₂, NO₃, OH and HO₂; and for their self-reactions and cross-reactions with other RO₂ radicals. This information is used to define generic rate coefficients and structure-activity relationship (SAR) methods that can be applied to the bimolecular reactions of a series of important classes of hydrocarbon and oxygenated RO₂ radical. Information for selected unimolecular isomerization reactions (i.e. H-atom shift and ring-closure reactions) is also summarised and discussed. The methods presented here are intended to guide the representation of RO₂ radical chemistry in the next generation of explicit detailed chemical mechanisms.