Bitter gourd (Momordica charantia) is a vegetable-cum-medicinal plant of Cucurbitacaeae family. It is a species under Momordica, a genus of Asiatic origin that exhibits immense species, phenotype, and trait diversity in warmer parts of Asia, including India, China, Thailand, Malaysia, and Indonesia. This is a crop for the future due to its immense nutraceutical values. In this chapter, the genetic resources of bitter gourd and the efforts dedicated toward its use in genetic improvement of the crop are thoroughly discussed. The chapter beings with its history, origin, and distribution. The debate about its origin and distribution to the New World is reviewed. The changes during domestication and morphological diversity between wild progenitor, South Asian and Southeast Asian cultivars is elaborated. The species diversity of Momorodica is thoroughly discussed in relation to gene pool concept based on its crossability behavior. The crossability works and barriers of interspecific and intergeneric gene transfer are analyzed. The economically important germplasm including local landraces, cultivars, and improved varieties are enlisted. Both phenotype-based and marker-based genetic diversity studies are reviewed. The recent advances in genetic mapping for identification markers linked to economically important traits such as gynoecy, earliness, fruit length, and fruit size in noble germplasm are covered. Hence, through this literature, we have attempted to put together all the genetic resources of bitter gourd that should be conserved, studied, and used for future breeding programs to evolve improved varieties.