Immunization is essential to disease prevention efforts in public health, but the nation's immunization system faces financing challenges that are affecting the delivery of services. A 2000 report from the Institute of Medicine (IOM), Calling the Shots: Immunization Finance Policies and Practices (IOM, 2000), pointed to the instability of the fundamental infrastructure that supports immunization programs throughout the United States, including unpredictable federal funding levels, growing financial burdens and operational complexities in immunization services, shortcomings in public- and private-sector investments in vaccine purchases and immunization programs, and fluctuations in coverage plans in the public and private health care sectors that create uncertainties regarding vaccine purchase and service delivery arrangements. In January 2002, health officials, public health experts, health care providers, health plan representatives, health care purchasers, and community leaders met at the University of California at Los Angeles to explore the implications of the IOM findings and recommendations for California in general and for Los Angeles and San Diego County in particular.The one-day workshop was the third in a series of four meetings organized by IOM with support from the Centers for Disease Control and Prevention to foster informed discussions about challenges for immunization finance and future financing strategies for immunization activities and the public health infrastructure that supports those activities. This report of the Los Angeles workshop summarizes the findings of the IOM study, reviews progress in responding to the IOM recommendations at the federal level, and highlights continuing challenges in immunization finance for the nation and at the state and local levels in California.