We propose that an employee's bottom-line mentality may have an important effect on social undermining behavior in organizations. Bottom-line mentality is defined as 1-dimensional thinking that revolves around securing bottom-line outcomes to the neglect of competing priorities. Across a series of studies, we establish an initial nomological network for bottom-line mentality. We also develop and evaluate a 4-item measure of bottom-line mentality. In terms of our theoretical model, we draw on social-cognitive theory (Bandura, 1977, 1986) to propose that supervisor bottom-line mentality is positively related to employee bottom-line mentality (Hypothesis 1). On the basis of conceptual arguments pertaining to bottom-line mentality (Callahan, 2004; Wolfe, 1988), we hypothesize that employee bottom-line mentality is positively related to social undermining (Hypothesis 2). We further predict a moderated-mediation model whereby the indirect effect of supervisor bottom-line mentality on social undermining, through employee bottom-line mentality, is moderated by employee core self-evaluations and conscientiousness (Hypothesis 3). We collected multisource field data to test our theoretical model (i.e., focal-supervisor-coworker triads; N = 113). Results from moderated-mediation analyses provide general support for our hypotheses. Theoretical and practical implications of bottom-line mentality and social undermining are discussed, and areas for future research are identified. (Contains 4 tables and 5 figures.)