Eggplants and related germplasm are a barely unveiled genetic treasure, for reasons developed in Chap. 10. Diversity and interspecific crossability researches focused so far on Solanum melongena L., the economic importance of which towers that of the indigenous African S. aethiopicum L. and S. macrocarpon L. and which consequently attracted most of geneticists’ and breeders’ attention. However, as S. melongena shares many connections with eggplant germplasm as a whole, this chapter pays as much attention to this species as to the other cultivated and wild ones. Their genetic and phenotypic diversity is surveyed and critically analysed in order to place the reader at the crossroads between the present knowledge and desirable future researches in terms of both traits of interest to breeders and methods for assessing the diversity. The dense corpus of information about interspecific crossability is organised across several axes. Conventional sexual crosses and somatic hybridisations are presented separately, given both methods yield genetically different interspecific material. The section devoted to sexual crosses begins with a survey of the interspecific barriers, and with an overview of the crossing results that are discussed in their methodological dimensions, in particular the criteria assessing the success or failure of the crossing experiments. Then, the crossing results are structured according to the combinations of crosses within and between cultivated and wild material. Species crossability is discussed with regard to the genepool concept and to relationship between species assessed by phylogenetics. The section ends up with interspecific hybrid by-products such as male sterilities and information on traits genetics. The chapter turns then to somatic hybridisations; this part is structured according to groups of species (e.g. New World species) used as fusion partners of S. melongena, the pivotal taxon for most of the fusion experiments. The conclusions outline the limits of the present knowledge on eggplants germplasm diversity and crossability and suggest potential new research routes on these topics.