The genus Brassica comprises some of the most economically important oilseed and vegetable crops cultivated worldwide. These crops contribute significantly to global food security, nutrition, and agricultural sustainability. The present paper provides a comprehensive synthesis of the origin, geographical distribution, and genetic diversity of major crop Brassica species. Archaeobotanical and molecular evidence suggests that primary domestication of diploid Brassica species (B. rapa, B. nigra, and B. oleracea) occurred independently in the Mediterranean and Central Asian regions between 3000–5000 years BP. These diploid species subsequently gave rise to amphidiploid species (B. juncea, B. napus, and B. carinata) through natural hybridization and polyploidization, as described by U’s Triangle. Genetic diversity studies using molecular markers (SSR, SNP, AFLP) reveal high intra-specific variation, particularly in B. rapa (Nei’s gene diversity, H = 0.42–0.65; derived from genome-wide SNP analyses by Bird et al., 2020 and Park et al., 2023) [1] and B. juncea (H = 0.38–0.60; reported using SNP and GBS approaches by Hasan et al., 2023 and Gupta et al., 2024), reflecting wide ecological adaptation. Understanding the origin, distribution, and diversity of crop Brassicas is essential for crop improvement, conservation of genetic resources, and climate-resilient breeding programs.