Research problem: Partially distributed teams (PDTs) are virtual teams that consist of at least two distinct geographically dispersed subgroups that communicate mainly through information and communication technology (ICT). As such teams become increasingly prevalent, it is important to understand how to manage them to maximize team effectiveness. The perceptions of effectiveness of PDTs may be significantly decreased when they are characterized by ingroup dynamics, consisting of preferential attitudes and actions toward collocated members, with accompanying conflict and lack of trust in regard to the distant subteam(s). Research questions: Do ingroup dynamics negatively impact perceptions of effectiveness in PDTs and, if so, how strongly? What factors can lessen ingroup dynamics-specifically, can training or reliable ICT support decrease ingroup dynamics? Does organizational context affect these relationships? Does whether or not the PDT is international affect these relationships? Does the number of subgroups in a PDT affect these relationships? Literature review: Social identity theory suggests how ingroup dynamics may emerge and create fault lines between subteams in a PDT. Effectiveness is defined in terms of process performance, which refers to how well the teamwork process has been undertaken. Prior research suggests that ICT reliability and training for work in distributed teams may decrease ingroup dynamics and improve effectiveness. International members, the specific organizational context, and the number of subteams per team might moderate these relationships. Methodology: An online survey of professionals with experience in PDTs was conducted, with two subsamples-one from a single large telecommunications company and one from a mix of organizations. Partial least squares regression was used to build and test a model of the relationships among the variables measured. Results: Ingroup dynamics have a strong negative relationship with perceived effectiveness. Overall, technology reliability and training significantly reduce ingroup dynamics. In the telecommunications company, training increased ingroup dynamics; thus, training may not always be beneficial, depending on organizational culture and the modes and types of training provided by a specific organization. Neither international membership on the team nor the number of subgroups per team was a significant multigroup moderator on any path in our model. Conclusions: These results help to extend social identity theory into this domain as they elucidate specifically that ICT reliability and training promote effectiveness of PDTs and that ingroup dynamics affect the perceptions of effectiveness in such teams. The results give managers guidance on what issues of PDTs to focus on to promote the effectiveness of PDTs.