The federal and state partnership in supporting immunization programs that benefit the general population evolved over the last half of the 20th century from a simple cost-sharing arrangement for vaccine purchase for disadvantaged children to a more complicated mix of programs, health care coverage benefits, and public-private partnerships. The mix of financial arrangements that support immunization efforts was the subject of a study by the Institute of Medicine, resulting in the publication of the report Calling the Shots. In June 2001, a group of 50 health officials, public health experts, health care providers, health plan representatives, and community leaders met at the University of Illinois in Chicago to explore the implications of the IOM findings and recommendations for the states of Illinois and Michigan. The one-day workshop was the first in a series of four meetings organized by IOM with support from the Centers for Disease Control and Prevention to foster informed discussions about future financing strategies for the public health infrastructure that supports immunization efforts.This report of the Chicago workshop summarizes the findings of the IOM study and reviews the challenges that remain in establishing a reliable financial base for the U.S. immunization system. The report high-lights strategies presented by workshop speakers and discussants for achieving immunization goals, including increases in state and federal public health budgets, the addition of quality improvement measures in health plans, performance-based contracting, public policy actions, and the creation of public-private partnerships.