Researchers have given considerable attention to the antecedents and outcomes of mistreatment at work including bullying, incivility, harassment, and subtle discrimination. However, the focus of much of this work has been on the role that mistreatment plays at the individual, dyadic, or organizational level. Given increased reliance on teamwork in organizations and the role that teamwork plays in the day-to-day experiences of members, I conducted two studies focused on teamwork process exclusion, which I define as failure to include a team member in teamwork processes when it is socially appropriate to do so. These studies explored the impact of gender, race, and demographic dissimilarity as antecedents of teamwork process exclusion; team member trust perceptions as an individual-level outcome of teamwork process exclusion; and trust dispersion as a team-level outcome of teamwork process exclusion. I also explored the role of negative affect in explaining the relationship between teamwork process exclusion and trust perceptions. Study 1 was a longitudinal study of 184 engineering design students working in 50 teams on a year-long project. Results from Study 1 indicated that individuals who tended to experience teamwork process exclusion generally felt lower levels of team trust. I did not find support for my hypothesis predicting that teamwork process exclusion would predict team trust dispersion; however, Study 1 did indicate that at the team level, teamwork process exclusion predicted lower mean levels of team trust. Study 2 expanded on Study 1 by exploring how teamwork process exclusion unfolds in the day-to-day using an experience sampling design with a sample of 152 full-time engineers. In Study 2, I found that participants’ ratings of teamwork process exclusion in the afternoon predicted higher levels of negative affect the same evening. Neither study provided evidence for the hypothesized relationships between gender, race, or demographic dissimilarity on incidence of teamwork process exclusion. Taken together, these studies indicate that teamwork process exclusion does relate to lower levels of trust and higher levels of negative affect, but that these phenomena may play out differently in the day-to-day than over the course of longer periods of time. In addition, Study 1 provides initial evidence that teamwork process exclusion may have important effects on the emergence of trust at the team level.