Although the Internet has spawned significant changes in communication and interpersonal behavior, the data concerning the social and psychological effects of its use are equivocal. Drawing on the uses and gratifications model of communications media, it was hypothesized that the social and psychological effects of Internet use depend primarily on the user's reasons and goals for using the technology. That is, the Internet's social and psychological effects depend upon the functions it serves for users. A theoretical model involving the functions of Internet use, dimensions of social integration, and dimensions of psychological well-being was examined. In study 1, participants indicated the primary reasons for which they use the Internet. Principle components analyses indicated that these reasons fell under two empirically robust dimensions accounting for about half of the total variance in Internet use. These dimensions, or functions, were labeled Socio-Affective Regulation (SAR) and Goods-and-Information Acquisition (GIA); SAR may be conceptualized as a social or an affiliative orientation toward Internet use, whereas GIA may be conceptualized as a utilitarian or practical orientation toward Internet use. In study 2, structural equation modeling revealed that Internet use driven by SAR negatively influences psychological well-being by first reducing social integration. However, Internet use motivated principally by GIA appears to have a favorable effect on psychological well-being by first increasing social integration. Implications of these results and directions for future research are discussed.