Guidelines are becoming increasingly important as potential tools in improving clinical decision making. Because oncology practice encompasses a large number of tumors and their variants and because each tumor is characterized by heterogeneous presentations and clinical evolutions, an oncology guidelines program must be large in scope. Oncology practice is slowly moving toward evidence-based status, but guideline developers still must rely on less than perfect information to achieve this scope. By formalizing the consensus process, the NCCN program relies on the expertise of a broad range of cancer specialists to interpret the major clinical studies and apply their evaluative skills in assessing the relevance of these studies to clinical practice. In areas in which data are meager or contradictory, these experts are still charged with making recommendations if they believe their collective clinical experience points to a reasonable approach to disease management. It follows, therefore, that guidelines represent one of the most dynamic areas in medicine. The annual review process is designed to incorporate change as new evidence or innovative therapies become available. Therefore, the guidelines should be a true reflection of the state-of-the-art in oncology. The ultimate goal, as always, is improving care for the cancer patient.