Social familiarity has been widely studied by researchers across a range of psychological disciplines, with level of familiarity in social context being indicated as a powerful factor influencing affective and motivational states. The degree of familiarity among drinking companions has further been linked to patterns of alcohol use, with regular drinking in unfamiliar social settings being associated with heavy consumption and drinking in highly familiar settings being indicated as a potentially protective factor. But social familiarity has received relatively little attention in relation to the psychological and cognitive processes supporting alcohol consumption. Here, in 2 studies, we explore the effects of social familiarity as it relates to alcohol expectancies—psychological processes believed to serve as among the most proximal determinants of alcohol consumption. In Study 1, we use a between-subjects design to explore the effects of familiarity in a sample of 400 undergraduates (40% male), producing evidence that individuals believe that alcohol consumption will be associated with significantly greater social enhancement and tension reduction when it is consumed in the company of unfamiliar versus familiar individuals. In Study 2 (N = 107; 41% male), we replicate these effects using a within-subject design and reveal effects of familiarity that are large in magnitude. Results of these studies provide initial evidence for familiarity among drinking companions as a factor driving beliefs surrounding alcohol’s effects, and indicate familiarity as a potentially promising line of inquiry for future research exploring determinants of drinking.