In alcoholism research, two fundamental and closely related questions are: "Why do people drink?" and "Why do some people drink too much?" Humans voluntarily drink alcoholic beverages or self-administer alcohol, more often than not, in a social setting. Environmental factors and how individuals react to them can, therefore, have powerful influences on drinking behavior. On the other hand, the neuropsychopharmacological actions of ethanol and how different individuals react to them can be important biological determinants. Ethanol's action is biphasic, i.e., it can be reinforcing (rewarding) in the low concentration range, but aversive at high concentrations. Perception by the individual of the reinforcing actions of ethanol might be expected to maintain alcohol-seeking behavior, whereas aversive effects would be expected to extinguish this behavior. Identification of the environmental and biological variables that promote and maintain alcohol-seeking or alcohol self-administration behavior is key to our understanding of the disorder alcoholism itself.