Immunization rates for children and adults are rising, but coverage levels have not reached optimal goals. As a result of low immunization rates, vaccine-preventable diseases still occur. In an era of increasing complexity of immunization schedules, rising expectations about the performance of primary care, and large demands on primary care physicians, it is important to understand and promote interventions that work in primary care settings to increase immunization coverage. A common theme across immunization programs in all nations involves the challenge of determining the denominator of eligible recipients (e.g. all children who should receive the measles vaccine), and identifying the best strategy to ensure high vaccination rates. Strategies have focused on patient-oriented interventions (e.g. patient reminders), provider interventions, and system interventions. One intervention strategy involves patient reminder and recall systems.