Among all genera belonging to the Cannabaceae family, C. sativa has attracted special interest from the public because of its psychoactive effects. The genetic plasticity of cannabis has made it difficult to catalog, and there is still an ongoing discussion about its proper classification. In 1737, Carl Linnaeus, the father of modern taxonomy, described C. sativa as a genus composed of a single species, C. sativa. Linnaeus was unaware of drug-type cultivars that were prevalent in Asia and classified cannabis as a single species from his experience with fiber-type crops that were common in Europe (Linnaeus, 1800). It is uncertain how he would have cataloged the new Indian and Asian cannabis cultivars had he been aware of them during his era. Comparative analyses between the Indian and the European hemp varieties, based on size, shape, leaf structure, and psychoactive effects, inspired Jean-Baptiste Lamark to classify the Indian cultivars as a separate species, Cannabis indica (Lamarck, 1811 ). The Soviet botanist Janischevsky revisited the polytypic (multi-species) view when he recognized that local Russian plants did not fit the characteristics of C. sativa or C. indica , but fell within the Cannabis taxa. He named the short, wild Russian autoflowering plants C. ruderalis (Small, 1975 ) and divided the genus into three distinct species, C. sativa L., C. indica Lam., and C. ruderalis Janisch. According to the American Herbal Pharmacopeia, C. sativa L. was historically bred to be tall and is used mainly for fiber and seed (Figure 53.1 ;Upton et al., 2014 ). C. sativa indica Lam. is characterized by a short, densely branched structure and potent level of Δ9 -tetrahydrocannabinol (Δ9 -THC), which is the main psychoactive ingredient (Upton et al., 2014 ). To date, scholars still disagree on how to correctly catalog cannabis species. The two competing schools of cannabis taxonomy are divided between a monotypic (single-species) and a polytypic perspective. The current debate centers on one question: Are all cannabis cultivars C. sativa ? Sativa and indica cannabis types are frequently crossbred to produce hybrid phenotypes with desired characteristics. The viability of interbred sativa and indica cannabis types supports the cataloging of all varieties as subspecies of C. sativa (i.e., C. sativa sativa ,C. sativa indica , and C. sativa ruderalis ) (Anderson, 1980; Schultes et al., 1974 ). To simplify the text, the monotypic subspecies nomenclature is used throughout this chapter.