Academic social networking (ASN) sites are becoming a popular communication medium among scholars. This case study was designed to explore communication behaviors of physicists, linguists, and sociologists on an ASN site called Academia.edu, their motivations for using it, and the perceived impact of their use of the site on their professional activities. Results from this study are valuable for designing computer-mediated and web-based communication media for scholars and also for adding richness to the literature related to scholarly communication. For the purpose of this study, data was collected using three different instruments: Server log, survey, and interview. Data used for analyses included a total of 20,309 server log data, 267 survey responses, and 28 interviews from scholars of Physics, Sociology, and Linguistics who use Academia.edu. Results from the study showed that the use of Academia.edu is dependent on the discipline scholars are affiliated with, their professional status, and the time of the year. Unlike physicists, linguists and sociologists are more inclined to using Academia.edu and other ASN sites. Although linguists and sociologists actively use Academia.edu, their motivations to use the site are different. These differences in user-motivations and user-activities across the disciplines are influenced by variations in the social and cultural practices of the disciplines. This study used Whitley’s (2000) theory of degrees of mutual dependence and task uncertainty to explain the differences in the adoption and use of Academia.edu across the three disciplines.