Substance use and substance use disorders (SUDs) occupy a critical nexus between medical, legal, and social systems. Historically, substance use has alternately been conceptualized as a criminal offense or a public health concern, reflecting shifting societal attitudes toward addiction and accountability. This chapter provides an overview of the evolution of substance use legislation in the United States, emphasizing the interplay between legal frameworks and clinical practice. It examines modern laws governing the treatment and classification of SUDs, the implications of insurance coverage for equitable access to care, and the social and ethical challenges arising from substance-related policies. The chapter also explores the integral role of substance use in forensic psychiatry, where legal standards and psychiatric evaluations converge. While comprehensive solutions to substance-related problems extend beyond the chapter’s scope, the discussion underscores the necessity of multidisciplinary, evidence-based approaches that address the biological, psychological, and sociocultural dimensions of addiction. Ultimately, substance use remains a persistent societal issue whose impact may be mitigated through continued advocacy, informed policy development, and collaboration across healthcare, legal, and community domains.