The National Research Mentoring Network - Resource Center (NRMN-RC) is a nationwide initiative that aims to broaden the participation of STEMM workforce through culturally-responsive mentorship, networking, and professional development. NRMN-RC initiated its Phase II in 2019 (previously named Mentorship and Networking Core, initiated in 2014). NRMN-RC is part of a larger diversity program consortium that includes STEMM, biomedical/behavioral professionals, and institutions collaborating to provide evidence-based mentorship and professional development programming. NRMN-RC supports individuals from all backgrounds, including individuals from historically marginalized backgrounds, across all career stages: undergraduate, graduate, and postdoctoral students; junior and senior faculty; professional researchers; and administrators in STEMM. Further, higher education institutions, minority-serving institutions (MSIs), professional/scientific societies, organizations, and other entities can leverage the NRMN-RC resources to mutually broaden participation in STEMM. NRMN-RC virtual resources include culturally responsive one-on-one mentoring, peer mentoring, courses, and professional development webinars to enhance mentoring relationships and skills. Our online platform (MyNRMN) has facilitated more than 11,700 unique mentoring connections. Mentors and mentees can video chat, join and/or create collaboration groups, build their curriculum vitae/resume, and search for jobs and opportunities. NRMN-RC includes a network of more than 30,000 mentors, mentees, and members across all 50 states and Puerto Rico, over 500 nationwide partners, and a subscriber list of over 35,000 individuals nationwide. More than 4,200 nationwide institutions have members in NRMN, including 190 MSIs.