Literature records of naturally occurring heterospecific pairs are summarized on a worldwide basis. The 93 pairs include: 11 between members of different families, 21 between different genera, 61 between different species. In all, 10 families, 34 genera, 124 species are represented. Anisoptera genera with the greatest number of species in the mixed pairs are Sympetrum and Gomphus; Zygoptera genera are Lestes and Enallagma. An important factor limiting the number of records of mixed pairs is difficulty in determining the females of many genera. Despite the seemingly numerous records and the taxonomic spread of the mixed pairs (actually only a small proportion of the entire Order), there are only two records of heterospecific pairs ovipositing and two (one very doubtful) of hybrids resulting from observed mixed pairs under natural conditions. The species of Odonata are apparently effectively isolated even though mixed tandems and mixed wheel positions do occur.