There is growing evidence that population health is influenced by broad socio-environmental factors that require population-focused health promotion strategies. The author reports on a study of the perspectives of public health nurses (PHNs) on the nature of their health promotion practice in the Canadian province of Manitoba, highlighting their perceptions about barriers to population-focused health promotion. A descriptive, exploratory research design was used to conduct standardized open-ended interviews with 24 PHNs in 3 geographically and demographically diverse health authorities. There were remarkable similarities in PHNs' perceptions about their practice. Three categories of barrier to population-focused health promotion were identified: barriers at the level of individual PHNs; organizational barriers (culture, policies, processes); and extra-organizational barriers at the level of the community or province. The results point to a gap between the theory that population-focused health promotion is at the heart of PHN practice and the experience of PHNs at the 3 sites. A concerted effort to address the barriers is needed so that PHNs in Manitoba can play a leadership role in creating a health-care system that truly invests in population health.