A growing sense of the need to define good-quality cancer care has emerged in the past decade of the 20th century. The goals were to assess, improve, and reward quality. Animated debates between cancer care delivery academic and community organizations, governmental agencies, and insurance companies have led to multiple initiatives and pilot projects. ASCO was on the cutting edge of quality in oncology movement. We can define three phases, overlapping rather than sequential, in ASCO's journey. The first phase was generating definitions of good-quality care characterized by the publication of ASCO guidelines. The second phase was the creation of the tools to measure the implementation of standards of care with the creation of the Quality Oncology Practice Initiative (QOPI). The third phase was the launch of a comprehensive approach to cancer care quality as illustrated by QOPI Certification, then the more complete iteration, ASCO Certified Program. The latter is the most elaborate program to define quality from the patient and health care providers' perspective on one hand and governmental agencies and insurance providers' perspective on the other. Since the publication of the Ensuring Quality Cancer Care Report in 1998 to the ASCO Certified in 2023, a quarter century has elapsed. ASCO did not operate in a vacuum. Through collaborative efforts, reacting to and interacting with various players, it has advocated for positive change. During this period, ASCO has led the movement of quality in oncology intelligently and with the upmost sense of responsibility toward the patients, health care professionals, and society at large. While many of these efforts began domestically, their reach is extending globally through research, education, and the promotion of equitable care.