The Inclusive STEM Teaching Project (ISTP) is an NSF-sponsored professional-development initiative consisting of an open online course that advances the awareness, self-efficacy, and abilities of current and future faculty members to cultivate inclusive STEM learning environments and to develop as reflective, inclusive practitioners. This poster will present the mixed-method research methodologies and measures used to understand the impact of the ISTP on program participants and emergent qualitative and quantitative findings. To date, the project has collected extensive survey and program data from three program cohorts to examine the achievement of learning outcomes. In addition, the project has conducted over 70 semi-structured interviews with participants from two cohorts to further investigate the impact of and the various ways participants have implemented what they have learned from the program in their campus instructional and leadership responsibilities. Overall, research data demonstrate substantial impact on program participants in advancing inclusive STEM teaching.