The need for public health awareness and evidence-based clinical care for marijuana use and its disorders remains a major health care priority in the United States and beyond. Indeed, marijuana has been the most widely used illicit substance in the United States for the past 30 consecutive years, with approximately 25 million people in the United States (8.6% of the population) having used marijuana in the past year. The overarching aim of the present chapter is to provide an overview of marijuana use and its disorders. The chapter is organized into seven sections. First, we describe the prevalence of marijuana use and its disorders. Second, we clarify the nature of marijuana use in terms of its pharmacokinetics and acute intoxication features. In the third section, we describe the classification of marijuana use and its disorders using the current diagnostic nomenclature. Fourth, we describe the motivational bases for use of the drug. In the fifth section, we provide a synopsis of some problems associated with marijuana use and its disorders, including health problems, social problems, and psychological disturbances. Sixth, we provide a summary of the scientific work focused on marijuana, the reasons for its use, and users’ relative success in quitting. In the final section, we describe some practically oriented clinical issues for primary care medical practitioners to consider in terms of the recognition and treatment of marijuana use and its disorders.