How does temporary mood influence the way people think and behave in social situations? Although most people are intuitively aware that feelings can have a profound influence on their thoughts, judgments and behaviors, we do not yet fully understand how and why these influences occur. This paper presents an integrative review of past and present ideas about the role of affect in social behavior, and offers a theoretical explanation of these effects based on the multi-process Affect Infusion Model (AIM; Forgas, 1995a). A series of programmatic experiments looking at affective influences on social thinking, judgments, and behaviors carried out in our laboratory will also be described. It will be argued that the different information-processing strategies people adopt in different situations play a key role in promoting, inhibiting, or even reversing affective influences on cognition and behavior. Indeed, the evidence to be reviewed here will suggest that it is the very complexity and indeterminacy of many social situations that promotes affective influences on interpersonal behaviors. The principle appears to be that the more complex and ambiguous a social situation, the more likely it is that people will need to engage in open, elaborate, and constructive thinking, drawing on their own memory-based ideas in order to produce an appropriate response. A number of theories as well as empirical studies now predict that such open, elaborate processing strategies are especially likely to be influenced by affective states (Fiedler, 1991; Forgas, 1995a).