This article examines the conditions under which members of academic Internet discussion groups (IDGs) are motivated to provide help and answers to colleagues during group discussions on the Internet. It presents a simple microeconomic model that specifies mechanisms by which the embeddedness of IDGs in academic social networks provides incentives for active participation of members during group discussions. According to the reputation model, the sending of public email messages is a means for the researcher to gain reputation in the academic community. Hypotheses of the models are tested with the help of data on the observed communication behaviour of researchers in 49 academic IDGs. The results provide some support for the hypotheses of the model. Most important, they show that the embeddedness of academic IDGs in social networks stimulates the active participation in online discussions. The findings contribute to filling an important gap. They help understand how offline networks influence online communication by showing which characteristics of offline networks have what impact. Conclusions are drawn for the social design of online groups.