This article outlines the history of federal immunization policy and funding, with a focus on discretionary federal funding under Section 317 of the Public Health Service Act, paying particular attention to the role of Congress in shaping the program in the past 2 decades. This review of funding trends and initiatives indicates that when both a presidential administration and key congressional actors viewed immunization as a priority and made sufficient funds available to support the public health delivery system and its infrastructure, coverage levels would continue to rise and disease levels continue to decline. From the beginning, immunization financing was explicitly structured as a federal-state-private-sector partnership. Section 317 program's statute has not changed much in 35 years, despite significant changes to the health care delivery system, other federal immunization activities, and rates of immunization coverage. Although the creation and implementation of the Vaccines for Children (VFC) program in the mid-1990s resulted in some congressional deliberations over immunization policies, no explicit restructuring of the 317 program occurred as a result. The Section 317 program retains its traditional authority and mission to address urgent needs, sustain public delivery systems, and provide funds for purchase of vaccines. The question remains whether the resources to sustain progress in immunization can be secured during times with no crisis, to ensure constant "readiness" in immunization (as in defense), or whether another epidemic must occur before the federal government is willing to commit optimal resources.