Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2, has produced significant acute and long-term health consequences worldwide. A subset of individuals experience persistent, recurrent, or newly developed symptoms after acute infection, commonly described as long COVID or post-COVID-19 condition. The World Health Organization defines post-COVID-19 condition as symptoms usually beginning within three months of initial infection and lasting at least two months, often affecting daily activities. Long-term effects may involve respiratory, cardiovascular, neurological, psychological, metabolic, renal, gastrointestinal, and musculoskeletal systems. Common manifestations include fatigue, dyspnea, cognitive dysfunction, sleep disturbance, chest pain, palpitations, anxiety, depression, post-exertional symptom worsening, and reduced quality of life. This review examines the long-term clinical effects of COVID-19, proposed mechanisms, risk factors, diagnostic approaches, management strategies, and public health implications. Current evidence suggests that long COVID is heterogeneous, fluctuating, and clinically complex, requiring multidisciplinary care, symptom-directed treatment, rehabilitation, prevention of reinfection, vaccination, and continued research.