Obstructive sleep apnoea (OSA) has emerged as a pervasive non-communicable disorder, now affecting roughly one in seven adults worldwide, with an estimated 425 million individuals suffering from moderate-to-severe disease. Prevalence shows striking geographic and ethnic variation—ranging from 8% to more than 70%—driven by disparities in obesity rates, craniofacial morphology, and access to diagnosis. Ageing populations, the global obesity pandemic, and male sex constitute the dominant risk triad, yet ethnicity-specific factors modulate this baseline: Asians develop OSA at lower body-mass indices due to craniofacial restriction, while African American patients display larger soft-tissue burdens despite less skeletal narrowing. Beyond anatomy, pathophysiological endotypes—including high loop gain, low arousal threshold, and impaired upper-airway muscle responsiveness—shape interindividual susceptibility. orofacial myofunctional disorders, present in up to half of school-aged children, further compromise airway development and portend adult OSA if uncorrected. Heritability studies suggest that ~30% of apnoea–hypopnea index variance is genetic, but risk loci differ between populations and remain below genome-wide significance thresholds. The societal cost of undiagnosed OSA is staggering—exceeding US $150 billion annually in the United States alone—through lost productivity, crashes, and cardiometabolic sequelae, with analogous burdens documented in Europe. This chapter synthesises the epidemiological, anatomical, physiological, genetic, and economic evidence to highlight knowledge gaps and underscores the need for culturally tailored screening, precision-medicine risk stratification, and early, multidisciplinary intervention.