Cannabis is the world’s most widely cultivated and consumed illicit drug. However, there remain major gaps in understanding the global cannabis markets. Assessing the extent and impact of the increased trend in cannabis is hampered both by a lack of international standard on issues such as terminology and by unanswered research questions. While there has been extensive research on the health effects of cannabis, there has been little academic study of the ways the drug is cultivated, dealt, and smoked. Therefore, many basic questions remain unanswered in the scientific and published literature. This review looks at some of the questions that have been asked and makes an attempt to answer them using a range of sources. The first part of the review looks at the technical aspects of cannabis production, in particular the modern innovations in indoor cultivation. The second part looks at cannabis consumption, reconciling supply-side and demand-side estimates. The third part of the review looks at what is known about cannabis markets in regions around the world, highlighting the universality of the problem. This is followed by a look at the impact of cannabis, focusing on two areas of primary concern: the recent increases in sinsemilla potency and their possible impact on treatment demand; and the recent findings of the scientific literature on the health effects of cannabis consumption. The review was prepared pursuant to General Assembly resolution 59/160 of December 2004 which requested the United Nations Office on Drugs and Crime to prepare a global market survey of cannabis. Tables, figures and references