This paper focuses on professional development within the GIS organization for individuals who make lateral moves or otherwise come into the field of GIS with a lack of knowledge and skills in one or more of five critical areas. This frequently occurs during department reorganizations, career development programs and internships. While many forms of training are available, mentoring can provide the kind of long-term training that promotes the application of knowledge and the mastery of complex skills that are essential to a robust GIS. This can be accomplished through projects designed around five areas: (1) spatial reasoning, (2) computer science, (3) cartography, (4) interdisciplinary fields, and (5) GIS management. The person being mentored acquires skills and knowledge in the first three areas, while the mentor often obtains skills and knowledge in the fourth area. Lastly, mentoring each person within the GIS organization in various aspects of GIS management promotes shared responsibility and a team-based approach to maintaining a robust GIS.