Engineers who are introverts and logic-based decision makers generally lack interpersonal skills. This deficit may inhibit them from moving into managerial leadership positions in the same proportion as extraverts. The research problem was an inadequate understanding about how introverted engineers who are logic-based decision makers develop interpersonal skills. The purpose of this study was to analyze and synthesize the experiences of introverted engineers who are logic-based decision makers on the evolution of their interpersonal skills in the areas of supportive communication, influence, conflict management, and motivating others. A qualitative multiple case study approach was used because of the nature of the proposed research problem and the limited knowledge in this area. Engineers who are introverted and logic-based decision makers were recruited through online groups whose membership is predominately engineers. Six volunteers who met the study criteria were interviewed—three typified the central case and three represented an alternate case. The research identified the process introverted engineers use when applying interpersonal skills. The overall process was very similar for all of the research questions. However, noteworthy differences between the central and alternate cases were observed for the conflict management and motivation research questions. The researcher concluded that a pre-existing knowledge base is fundamental to skill development for introverted engineers. As part of that knowledge base, these engineers need to know reflection, observation, and systems thinking skills. For conflict management skills, a key result was the importance of learning a strategy that keeps conflict focused on evidence. For motivation skills, the implication was that learning how to employ intrinsic rewards is essential. The researcher recommended that formal training in interpersonal skills be developed for introverted, logic-based engineers. In addition, the researcher recommended that organizations provide network expansion opportunities to build a cohort of coaches, mentors, and peers for their introverted engineers. Future research might look at the components of interpersonal skills training delivery for this audience, the effects of gender on the results, and whether managerial success/effectiveness changes the patterns for applying interpersonal skills.