A general survey of the chemistry of oxaziridines is presented, previous studies on the mechanism of the acid and base catalysed hydrolysis are critically reviewed and the results discussed in relation with the hydrolysis of compounds with related structures. Results of the acid hydrolysis of several oxaziridines are reported and agree with previous findings. These accord with a mechanism involving the breakdown of an 0-conjugate acid intermediate to give either a carbonium ion or an immonium ion structure, which subsequently reacts-with water. The importance of each pathway depends on the nature of the 3-substituent. The proton α to the ring nitrogen seems to be involved in the rate determining step for the reaction of 2-primary-alkyl 3-alkyl oxaziridines. For 2-secondary-alkyl 3- alkyl compounds extensive migration of an α group occurs and steric requirements and migratory aptitudes seem to be important. Investigations of the site of protonation suggest N as the most likely site, although hydrolysis probably proceeds via the 0-conjugate acid: pKA values for oxaziridines reflect the nature of the 3-substituent as well as the degree of branching at position 2 and lie in the range -1.9 to +0.30. Results of basic hydrolysis of several oxaziridines are reported and are consistent with earlier findings. The hydrolytic mechanism 'which rationalisesall the data is a heterolytic bimolecular rate determining abstraction of an 0( proton to the ring nitrogen by the base.