Echoing the rise of 'evidence-based medicine', the concept of evidence-based policy and practice in the inter-related fields of health promotion, public health and health improvement has attracted increasing attention over the past two decades. More recently, again with roots traceable to biomedical thinking, there has been growing interest in ethics in relation to these fields. This paper links these two topical themes in a practical way. It explores the extent to which policies and activities 'on the ground' can and should be based on evidence, and considers the relative places of evidence and ethics in decision-making. It goes on to present the 'decision-making triangle', a framework that gives primacy to a set of ethical principles--with available evidence and plausible theory being used to inform the application of these. After introducing the concept of 'ethical logic modelling', the paper concludes by suggesting an 'ethical imperative' for health promotion, public health and health improvement: to make decisions based on the explicit application of ethical principles, using available evidence and theory appropriately.