Science, technology, engineering, and math (STEM) mentoring programs typically have the goals of generating interest and excitement in STEM topics and careers and supporting STEM career achievement persistence. These outcomes are fostered through positive and trusting relationships with mentors. Mentors in STEM programs often have extensive subject matter expertise in a STEM content area, but they may lack the knowledge, attitudes, and skills that are important for establishing an effective mentoring relationship with a young person. The purpose of this review is to describe (1) a set of topics recommended for inclusion in STEM mentor training, based on a literature review, and (2) the current state of implementation of these recommended training topics among STEM mentoring programs in the United States. We have identified four major topic areas to include in the training of STEM mentors: (1) knowledge and attitudes regarding disparities in STEM career achievement, (2) mentor roles that promote STEM outcomes, (3) behaviors to promote mentees’ positive attitudes about STEM, and (4) program‐specific topics. Training for mentors should prepare them with the knowledge they need to support their mentee being successful in a STEM education or career while fostering the skills they need to establish an effective mentoring relationship.