Recent concerns about childhood vaccines such as the measles, mumps and rubella (MMR) vaccine have led to reduced vaccine uptake and increased probability of disease outbreaks. Psychological aspects of parental decision-making about vaccines are reviewed. Inconsistencies and gaps in the literature are highlighted and implications of what is known for public health are outlined. A decision theory model of the decision to vaccinate fits the facts well and generates practical strategies for uptake of MMR and similar childhood vaccines.