This critical review of literature on mentoring encompasses print and online books and journals from the mid-nineties on. While by no means comprehensive, the literature surveyed was adequate to indicate how the field of mentoring in education stands today. The author's particular focus, in response to her needs and goals as an educator, was on mentoring to facilitate the professional growth of teachers in-service, meaning those she would describe as mature professionals. The work that best represented the role that mentoring might play in the new professional and educational futures was that of Hargreaves and Fullan (2000). The author will use their journal article as the organising framework for this review, situating other works with respect to it. Hargreaves and Fullan refer to four evolutionary "ages" of professionalism, and link in associated approaches to mentoring. A personal caveat here is that these ages should not necessarily be seen as sequential in a linear way, even given Hargreaves and Fullan's timelining. There could be differentials in progress and development across various peoples, organizations, and cultures, making ages co-existent.