This paper presents the results of a preliminary structural survey of the ejaculates of representatives of all major odonate taxonomic groupings. Members of the Zygoptera, Libellulidae and the Corduliidae transfer individual spermatozoa whilst males of the remaining taxa inseminate females with spermatodesms (aggregated sperm) and varying degrees of free spermatozoa. The distribution of spermatodesm use across the reviewed taxa shows a relationship with various aspects of male and female reproductive behaviour. A function for odonate spermatodesms based on this relationship is suggested, and preliminary evidence consistent with the major prediction from this hypothesis is provided.