This article is a review of the effects of simple exposure on preferences for lights, tastes, social companions, and miscellaneous other stimuli. In all categories of stimuli, substantial support is found for Zajonc's hypothesis that mere exposure increases preference, but all categories also show evidence of reduced preference following exposure. Which of these effects will dominate appears to depend on different factors for different categories of stimuli. However, most of the findings are consistent with a model in which exposure produces both a long-term increase in preference (more rapidly in some stimulus modalities than in others) and a short-term decrease in preference.How do our preferences among stimuli-that is to say, our likes, dislikes, tastes, and interests-develop and change? In attempting to answer this question, learning theorists have traditionally focused on paradigms that involve pairing of two stimuli, under such rubrics as classical conditioning, secondary reinforcement, and learned drive. Recently, however, there has been increasing interest in paradigms that involve simply the repeated presentation of a given stimulus without its being paired with anything in particular. The greatest impetus to this interest has come from the work of Zajonc and his collaborators on mere exposure, starting with Zajonc's (1968) study. Also relevant are Solomon and Corbit's (1974) work on the temporal dynamics of affect, the study of habituation (e.g., Groves & Thompson, 1970;Leibrecht, 1974), and various other lines of theory and research.