Alcohol use disorder (AUD) includes alcohol abuse and alcohol dependence. Since AUD is considered a bio-psycho-social disease, the etiology is multifactorial, including biological, psychological and social variables. Neurobiologically, addiction is related to the ventral tegmental area and nucleus accumbens, known as the "pleasure center," and an imbalance of various neurotransmitters such as dopamine, gamma-amino-butyric acid (GABA), and glutamate. Psychologically, chronic drinking is used as a means of self-medication for reducing tension and stress and overcoming anxiety and depression. Socially, the rate of alcoholism depends on the culture and social attitude toward drinking behaviors. Social learning and conditioning are the social causes of AUD. Common clinical features of AUD include physiological changes such as tolerance and withdrawal, and occupational and social dysfunction. AUD is also closely associated with physical illness, such as alcoholic liver disease, thyroid dysfunction, and cardiovascular diseases. Understanding the etiology and clinical features of AUD is the first step to managing patients with alcohol problems. Physicians should consider alcohol abuse as a serious alcohol-related disorder that impairs familial, social, and occupational functions as much as alcohol dependence.