[Truncated abstract] Current literature about university teaching argues that online teaching requires online social learning based on social interaction to be effective. This implies a shift in pedagogy based on engagement and collaboration, instead of trying to reproduce face-to- face teaching, in online environments. However, when a university adopts an elearning platform (or Learning Management System, LMS), most teachers tend to reproduce their traditional teaching, delivering, through the LMS, educational material. This study explored factors which influence university teachers to adopt teaching models based on online social interaction (OSI) when an e-learning platform is used to complement undergraduate classroom teaching. Online teaching model adoption was considered in the framework of technology adoption and post-adoption behavior, i.e., adoption and use by individuals after an organization has adopted an ICT-based innovation (Jasperson, Carter, & Zmud, 2005). Behaviors were investigated using a model based on Ajzen's (1991) Theory of Planned Behavior (TPB). In total, 26 university teachers 15 from Australia and 11 from Italy holding undergraduate courses, were recruited. They responded to a semi-structured interview based on the TPB, built on purpose for this research. Teachers were divided into three different groups on the basis of their approach to online teaching, corresponding to three different levels of adoption of OSI. The three different online teaching models were: