Buyer decision processes are the decision making processes undertaken by consumers in regard to a potential market transaction before, during, and after the purchase of a product or service.

More generally, decision making is the cognitive process of selecting a course of action from among multiple alternatives. Common examples include shopping and deciding what to eat. Decision making is said to be a psychological construct. This means that although we can never "see" a decision, we can infer from observable behaviour that a decision has been made. Therefore we conclude that a psychological event that we call "decision making" has occurred. It is a construction that imputes commitment to action. That is, based on observable actions, we assume that people have made a commitment to effect the action.

In general there are three ways of analysing consumer buying decisions. They are:

• Economic models - These models are largely quantitative and are based on the assumptions of rationality and near perfect knowledge. The consumer is seen to maximize their utility. See consumer theory. Game theory can also be used in some circumstances.
• Psychological models - These models concentrate on psychological and cognitive processes such as motivation and need recognition. They are qualitative rather than quantitative and build on sociological factors like cultural influences and family influences.
• Consumer behaviour models - These are practical models used by marketers. They typically blend both economic and psychological models.

Nobel laureate Herbert Simon sees economic decision making as a vain attempt to be rational. He claims (in 1947 and 1957) that if a complete analysis is to be done, a decision will be immensely complex. He also says that peoples' information processing ability is very limited. The assumption of a perfectly rational economic actor is unrealistic. Often we are influenced by emotional and non-rational considerations. When we try to be rational we are at best only partially successful.

references and some content from Wikipedia