Every patient with cancer deserves access to evidence-based tobacco cessation interventions as part of their routine oncology care. The NCI Cancer Moonshot funded the Cancer Center Cessation Initiative (C3I) to help establish and/or expand tobacco treatment programs at 52 NCI-designated Cancer Centers. Although this initiative has broadened the availability of tobacco treatment services across US cancer centers, the reach and utilization of these services remains low among patients. To help address the remaining gap between the availability and utilization of evidence-based treatments for tobacco use in the oncologic context, staff and investigators at C3I sites and the C3I Coordinating Center formed the C3I Implementation Science Working Group. The mission of this working group is to bring together clinicians, scientists, and policymakers who share a common interest in implementation science and treating tobacco use in the oncologic context to collaborate on projects aimed at shrinking the practice gap in this area. Through case study examples, we describe how the C3I Implementation Science Working Group is supporting efforts to identify effective ways to increase the utilization of evidence-based tobacco treatments within cancer treatment settings and promote the broader impact and long-term sustainability of C3I.