With more than 25,000 professional nurse members, the Oncology Nursing Society (ONS) is the largest oncology membership organization in the world. Now in its 20th year, one way that ONS supports its mission of promoting excellence in oncology nursing is through the development and dissemination of patient care standards and guidelines. The first guidelines to be developed by ONS were the Cancer Chemotherapy Guidelines. Now in their third edition, the historical development and revision of these guidelines is detailed in this article, along with the evaluation and refinement of the process utilized by ONS.