Project Summary/Abstract This administrative supplement seeks to build upon our MIRA R35 award by developing and evaluating an innovative online course aimed at building mentorship networks within the biomedical sciences, particularly through the National Research Mentoring Network (NRMN). Aim 1 of the proposal is dedicated to the creation of a comprehensive five-module course designed to equip more than 300 researchers across all career stages with the skills necessary for effective mentorship and network building. These modules will cover foundational concepts of mentorship, strategies for self-assessment and goal setting, practical approaches for forming and sustaining mentorship networks, and insights into becoming impactful mentors themselves. Aim 2 focuses on evaluating the shift in participants' perceptions regarding the importance of mentorship and diverse mentorship networks, utilizing pre- and post-course surveys to measure impact. Aim 3 will assess how the course influences the development and enhancement of mentorship networks, tracking the formation of new connections and the improvement of existing ones, thereby facilitating a more inclusive and equitable biomedical research environment for potentially thousands of researchers. Through this supplement, we aim to address critical gaps in mentorship practices, fostering a culture of supportive, productive mentorship networks within the NRMN and beyond.