BACKGROUND: The National Horizon Scanning Centre provides national policy-makers in England with forewarning about emerging and new health technologies. This includes public health interventions (PHIs) but identification of these interventions is not always easy. OBJECTIVES: The aim of this study was to explore the meaning and define innovation in public health. METHODS: We used a quasi-Delphi method with questionnaire 1 sent to 106 public health and horizon scanning professionals and decision-makers in June 2008. Questionnaire 2 was developed based on answers to questionnaire 1 and sent to all respondents. RESULTS: A definition of innovative PHIs was developed: 'Innovative PHIs are generally new and different to established interventions. They should be equitable, applicable to all in a population, cost-effective and may address health determinants in the non-health sector of society. A good evidence base is ideal, but sometimes it may be necessary to consider PHIs lacking evidence'. Sources suggested for identifying innovative PHIs were similar to those used for other types of health technologies. CONCLUSION: Our findings should help early awareness and alert systems distinguish innovative from non-innovative PHIs, although its application in practice needs trialling.