When situations occur in which unwanted events are rightly or wrongly connected with vaccination, they may erode confidence in vaccines and the authorities delivering them. This document presents the scientific evidence behind WHO’s recommendations on building and restoring confidence in vaccines and vaccination, both in ongoing work and during crises. The evidence draws on a vast reserve of laboratory research and fieldwork within psychology and communication. It examines how people make decisions about vaccination; why some people are hesitant about vaccination; and the factors that drive a crisis, covering how building trust, listening to and understanding people, building relations, communicating risk and shaping messages to the audiences may mitigate crises. This document provides a knowledge base for stakeholders who develop communication strategies or facilitate workshops on communication and trust-building activities in relation to vaccines and immunization, such as immunization programme units, ministries of health, public relations and health promotion units, vaccine safety communication trainers and immunization advisory bodies.