Recent, rapid changes in recommendations regarding vaccination represent challenges for busy clinicians who need to be familiar with new developments. This article reviews the current age-based recommendations that are fundamental to the United States vaccine program, as well as current recommendations regarding contraindications, precautions, administration techniques, and storage procedures for routinely administered vaccines. The 2003 Recommended Childhood Immunization Schedule, the 2002-2003 Recommended Adult Immunization Schedule, contraindications for immunization, and general guidelines on immunization procedures are presented. Recent changes in recommendations for children are instituting thimerosal-free hepatitis B vaccine as soon after birth as possible (before hospital discharge) and encouraging immunization of all children aged 6 to 23 months against influenza.