Brassica species have an economic and medicinal importance. Estimation of the amount and distribution of genetic diversity within Brassica species is essential for establishing efficient management, conservation and breeding practices. This review discusses the taxonomy, gene pool, and Brassica-derived phytochemicals and their nutraceutical importance. It also surveys the recently advanced studies of the genetic diversity and phylogenetic studies of Brassica species at the level of morphological, cytological, biochemical and molecular markers that have proven to be useful for evaluating the genetic variation, taxonomic relationships and species identity, and could be useful for improving Brassica crops through future promising breeding programmes.