Many hundreds of household and industrial products can be volatilized readily and are subject to abuse. Inhalant abuse research has been hampered by a lack of consensus on whether or not there are subclassifications of abused inhalants based on chemical structure, form or intended use of the product or pharmacological properties. This paper discusses strengths and weaknesses of various approaches to classification of inhalants and suggests areas for future research in this area. It is concluded that classification of inhalants by form or product types is not useful for scientific purposes; rather, subclassification of inhalants should be based on a yet-to-be-determined combination of chemical and pharmacological similarity and shared patterns of abuse. One of the ways in which we can improve our understanding of inhalant abuse is to obtain more detailed information on individual products and chemicals, their patterns of use and the geographical distribution of their use.