The health promotion best practices literature is imbued with hope for knowledge mobilization, enhanced practice, and improved population health. Given constrained medical care systems, health promotion is key to reducing the significant burden of chronic disease. However, we have seen little evidence of change. This article investigates facilitators of, and barriers to, three stages of health promotion practice in public health organizations, interagency coalitions, and volunteer committees. The article focuses not on what works but why it does or does not, drawing on five case studies within the Canadian Heart Health Initiative. Results indicate that the presence or absence of appropriately committed and/or skilled people, funds and/or resources, and priority and/or interest are the most common factors affecting all stages of health promotion practice. The article extends the literature on internal and external factors affecting health promotion and highlights strategic influences to consider in support of effective health promotion practice.