Alcohol, primarily in the form of ethyl alcohol (ethanol), has occupied an important place in the history of humankind for at least 8000 years. In Western society, beer and wine were a main staple of daily life until the 19th century. These relatively dilute alcoholic beverages were preferred over water, which was known to be associated with acute and chronic illness. As systems for improved sanitation and water purification were introduced in the 1800s, beer and wine became less important as components of the human diet, and the consumption of alcoholic beverages shifted toward their present-day role (in many societies) as a socially acceptable form of recreation.

Ethanol is a weakly charged molecule that moves easily through cell membranes, rapidly equilibrating between blood and tissues. The level of alcohol in the blood is expressed as milligrams or grams of ethanol per deciliter (e.g., 100 mg/dL or 0.10 g/dL); a level of 0.02 to 0.03 results from the ingestion of one to two typical drinks. In round figures, 340 mL (12 oz) of beer, 115 mL (4 oz) of nonfortified wine, and 43 mL (1.5 oz) (a shot) of 80-proof beverage each contain ~10 to 15 g of ethanol; 0.5 L (1 pint) of 86- proof beverage contains ~160 g (about 16 standard drinks), and 1 L of wine contains ~80 g of ethanol.

Alcohol use is highly prevalent in most Western countries, with the 1994 per capita consumption in adults in the United States estimated at 2.17 gallons of absolute alcohol.

In most Western societies, at least 90% of people consume alcohol at some time during their lives, and 30% or more of drinkers develop alcohol-related life problems. Severe alcohol-related life impairment, alcohol dependence (alcoholism), is observed at some time during their lives in 10% of men and 3–5% of women, with an additional 5–10% of each sex developing persistent but less intense problems that are diagnosed as abuse.

The Diagnostic and Statistical Manual of Psychiatric Disorder (DSM-IV- TR) criteria for substance (including alcohol) dependence:

A maladaptive pattern of substance use, leading to clinically significant impairment or distress, as manifested by three (or more) of the following, occurring at any time in the same 12-month period:
(1) tolerance, as defined by either of the following:
(a) a need for markedly increased amounts of the substance to achieve intoxication or desired effect
(b) markedly diminished effect with continued use of the same amount of the substance
(2) withdrawal, as manifested by either of the following:
(a) the characteristic withdrawal syndrome for the substance (refer to Criteria A and B of the criteria sets for withdrawal from the specific substances)
(b) the same (or a closely related) substance is taken to relieve or avoid withdrawal symptoms
(3) the substance is often taken in larger amounts or over a longer period than was intended
(4) there is a persistent desire or unsuccessful efforts to cut down or control substance use
(5) a great deal of time is spent in activities necessary to obtain the substance (e.g., visiting multiple doctors or driving long distances), use the substance (e.g., chain-smoking), or recover from its effects
(6) important social, occupational, or recreational activities are given up or reduced because of substance use
(7) the substance use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance (e.g., current cocaine use despite recognition of cocaine-induced depression, or continued drinking despite recognition that an ulcer was made worse by alcohol consumption)

Criteria for substance (including alcohol) abuse

A. A maladaptive pattern of substance use leading to clinically significant impairment or distress, as manifested by one (or more) of the following, occurring within a 12-month period:
(1) recurrent substance use resulting in a failure to fulfill major role obligations at work, school, or home (e.g., repeated absences or poor work performance related to substance use; substance-related absences, suspensions, or expulsions from school; neglect of children or household)
(2) recurrent substance use in situations in which it is physically hazardous (e.g., driving an automobile or operating a machine when impaired by substance use)
(3) recurrent substance-related legal problems (e.g., arrests for substance- related disorderly conduct)
(4) continued substance use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of the substance (e.g., arguments with spouse about consequences of intoxication, physical fights)

B. The symptoms have never met the criteria for substance dependence for this class of substance.

Diagnostic criteria for alcohol withdrawal:

A. Cessation of (or reduction in) alcohol use that has been heavy and prolonged.
B. Two (or more) of the following, developing within several hours to a few days after Criterion A:
(1) autonomic hyperactivity (e.g., sweating or pulse rate greater than 100)
(2) increased hand tremor
(3) insomnia
(4) nausea or vomiting
(5) transient visual, tactile, or auditory hallucinations or illusions
(6) psychomotor agitation
(7) anxiety
(8) grand mal seizures
C. The symptoms in Criterion B cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.
D. The symptoms are not due to a general medical condition and are not better accounted for by another mental disorder.

The likelihood of withdrawal symptoms if intake is suspended, is experienced by 4.4 percent of Americans.

Alcohol dependence often has a familial pattern, and it is estimated that 40%-60% of the variance of risk is explained by genetic influences. The risk for alcohol dependence is three to four times higher in close relatives of people with alcohol dependence. Studies of isolated twins and adopted children and of families in general have confirmed a heritable component to alcoholism that seems greater in men than in women and is greater in identical twins than in fraternal twins.

Alcohol dependence and abuse are often associated with dependence on, or abuse of, other substances (e.g., cannabis; cocaine; heroin; amphetamines; the sedatives, hypnotics, and anxiolytics; and nicotine). Alcohol may be used to alleviate the unwanted effects of these other substances or to substitute for them when they are not available. Symptoms of depression, anxiety, and insomnia frequently accompany alcohol dependence and sometimes precede it.

In the U.S., the cost to society of alcohol misuse is about 100 billion dollars every year. These costs include expenditures on alcohol-related problems and opportunities that are lost because of alcohol.