Despite many recent advances in vaccine delivery, the goal for universal immunization set in 1977 has not been reached. In 2001, only 77.2% of US toddlers 19 to 35 months of age had received their basic immunization series of 4 doses of diphtheria and tetanus toxoids and acellular pertussis (DTaP) vaccine, 3 doses of inactivated poliovirus vaccine, 1 dose of measles-mumps-rubella (MMR) vaccine, and 3 doses of Haemophilus influenzae type b (Hib) vaccine. Children who are members of a racial or ethnic minority, who are poor, or who live in inner-city or rural areas have lower immunization rates than do children in the general population. Additional challenges to vaccine delivery include the introduction of new childhood vaccines, ensuring a dependable supply of vaccines, bolstering public confidence in vaccine safety, and sufficient compensation for vaccine administration. Recent research has demonstrated specific and practical changes physicians can make to improve their practices' effectiveness in immunizing children, including the following: 1) sending parent reminders for upcoming visits and recall notices; 2) using prompts during all office visits to remind parents and staff about immunizations needed at that visit; 3) repeatedly measuring practice-wide immunization rates over time as part of a quality improvement effort; and 4) having in place standing orders for registered nurses, physician assistants, and medical assistants to identify opportunities to administer vaccines. Pediatricians should work individually and collectively at local and national levels to ensure that all children receive all childhood immunizations on time. Pediatricians also can proactively communicate with parents to ensure they understand the overall safety and efficacy of vaccines.