The Archives will devote its April 2009 issue to research on vaccines and immunization. We are interested in original articles, systematic and narrative reviews, and commentaries on a variety of topics related to immunization of infants, children, and adolescents. These include vaccine trials, safety and effectiveness, interventions to increase immunization rates, analysis of the economic and other barriers to timely immunization, costs and cost-effectiveness of recently recommended vaccines, and ethical issues related to vaccines. Papers received by September 15, 2008, will have the best likelihood of being included in this theme issue.