The chemistry of heterocyclothiazenes is surveyed, with particular emphasis being placed on the dithiazine heterocyclic class. The known synthetic routes to dithiazines are discussed and the chemical, physical and spectroscopic properties of these heterocycles are reviewed. A wide range of novel 1,4,2-dithiazine derivatives have been efficiently synthesised, the key synthetic step being nitrogen ring expansion of 1,3-dithiolium cation salts by iodine-ammonia methodology. The utility and scope of this methodology have been developed. A variety of analytical techniques have been used to characterise the 1,4,2-dithiazines. Notably, the first X-ray crystal structures of the heterocycle are presented. Mechanisms for the ring expansion reaction are discussed. Reactions of 1,4,2-dithiazines have been extensively studied; the compounds act as precursors to a variety of other heterocyclic systems (isothiazoles, dithiins and thiophenes), and provide access to useful synthetic intermediates (mono-protected 1,2- di thiols).The iodine-ammonia approach has also been used to synthesise derivatives of the rare 1,2,3-dithiazine system, representing the first chemical route to this heterocycle. In related studies, the X-ray crystal structure of a l,2-dithiole-3-thione is described; the molecule is characterised by a three-dimensional array of non-bonded intermolecular close sulphur-sulphur contacts.