Despite considerable research on both adoption and diffusion of IS/IT innovations, there is a lack of coherent understanding of the processes by which innovations diffuse within social systems. This research proposes that the nature of the innovation diffusion process will depend on the characteristics of the innovation, the personal attributes of the individual, the interpersonal relationships, the composition of the social networks, and the specific influence tactics used by individuals. The empirical investigation involves a combination of three different research methods: meta-analysis, interpretive case studies, and simulation. The meta-analysis, at the organizational level, identifies the various factors (individual, dyad, social network, organization, and innovation) that affect innovation diffusion and their effect sizes. The interpretive case studies, at the social network level, help understand the interpersonal processes underlying innovation diffusion. The simulation, at the dyad level, traces how an individual’s adoption behavior may be affected by the combination of different influence tactics over time. Finally, findings from the three research methods will be synthesized to provide an overall understanding of innovation diffusion processes. This research should provide valuable insights into the ways in which IS/IT innovations diffuse within social networks, and how the diffusion processes vary depending on the nature of the IS/IT innovation, the influence tactics used by individuals within the social system, and the contingency factors relating to the dyad, network, and organization.