The central argument in this paper is that "public trust" is critical for developing and maintaining the health and wellbeing of individuals, communities, and societies. I argue that public health practitioners and policy makers need to take "public trust" seriously if they intend to improve both the public's health and the engagement between members of the public and public health systems. Public health practitioners implement a range of services and interventions aimed at improving health but implicit a requirement for individuals to trust the practitioners and the services/interventions, before they engage with them. I then go on to provide an overview of the theory of trust within sociology and show why it is important to understand this theory in order to promote trust in public health services. I then draw on literature in three classic areas of public health-hospitals, cancer screening, and childhood immunization-to show why trust is vital in terms of understanding and potentially improving uptake of services. The case studies in this paper reveal that public health practitioners need to understand the centrality of building and maintaining trusting relationships with patients/clients because people who distrust public health services are less likely to use them, less likely to follow advice or recommendations, and more likely to have poorer health outcomes.