Recently we argued that social justice is concerned with human well-being, which is best understood as involving plural, irreducible dimensions, each of which represents something of independent moral significance. Health is one of these, distinct dimensions of well-being, as is personal security, the development and exercise of cognitive capacities for reasoning, living under conditions of social respect, developing and sustaining deep personal attachments, and being able to lead self-determining lives. In this paper, we address why considerations of justice, and not utilitarian aims as applied narrowly to health outcomes, are most foundational to public health, In particular, we argue that the aspiration for improvement of the health of populations defines the positive aim of justice in public health, along with the negative aim of reducing or combating systematic disadvantage that affects adversely historically situated social groups and, more generally, children across the normal life span when their well-being is not assigned a special priority in the development of public health policies.