Public health literacy is an emerging concept necessary to understand and address the broad array of factors, such as climate change, globalization, and poverty, that influence the public's health. Whereas health literacy has traditionally been operationalized as an individual-level construct, public health literacy takes into account the complex social, ecologic, and systemic forces affecting health and well-being. However, public health literacy has not yet been fully articulated. This paper addresses this gap by outlining a broad, new definition of public health literacy. This definition was developed through an inductive analytic process conducted in 2007 by a multidisciplinary research team, and two expert-panel sessions were convened to assess the consensual validity of the emergent definition. Based on this process, public health literacy is defined as the degree to which individuals and groups can obtain, process, understand, evaluate, and act on information needed to make public health decisions that benefit the community. Three dimensions of public health literacy--conceptual foundations, critical skills, and civic orientation--and related competencies are also proposed. Public health literacy is distinct from individual-level health literacy, and together, the two types of literacy form a more comprehensive model of health literacy. A five-part agenda is offered for future research and action aimed at increasing levels of public health literacy.