The field of program evaluation has deemed interpersonal competencies as important and has included them as an essential competency domain for program evaluators; however, little is known about how evaluators develop and use interpersonal competencies. The purpose of this study was to explore interpersonal competency development and use by evaluators. This was completed through a comparative analysis of the interpersonal competencies included in existing sets of evaluator competencies, a review of competency structures from other professions, and interviews with experienced evaluators. First, the interpersonal competencies essential to evaluation practice were explored to further validate those included in the draft American Evaluation Association Evaluator Competencies (AEAEC). Results supported the inclusion of the current interpersonal competencies in the draft AEAEC and provided additional competencies that emerged through the comparative analysis. Second, this study attempted to better understand the ways in which interpersonal competencies are developed by experienced evaluators. As a result, experienced evaluators described developing interpersonal competencies in four ways, including through the practice of evaluation, formal education experiences, professional development opportunities, and life experiences. Third, this study attempted to illuminate some of the interpersonal competency development needs among new evaluators. Findings suggest that novice evaluators typically need further development in several interpersonal competencies and that these competencies are also assessed in the hiring process. Fourth, the potential ways to structure the AEAEC to promote use of the interpersonal competencies were explored. Through the review of competency structures, four potential ways to structure them emerged, including by categorizing competencies, job function, level of expertise, and developmental level.