Immunization during pregnancy with currently recommended vaccines prevents infection in the mother, the unborn fetus, and the young infant, and there is an increasing focus from different stakeholders to use this approach for other infections of importance to protect these vulnerable groups. The aim of this Maternal Immunization book is to provide a contemporary overview of vaccines used in pregnancy (and the lactation period), with emphasis on aspects of importance for the target groups, namely, rationale for the use of vaccines in pregnancy, safety, immunogenicity (immunology), timing to vaccinate, repeat doses, protective effects in the mother, fetus, and infant, and public acceptance and implementation, of existing and of future vaccines.