Increased focus on prevention presents health promoters with new opportunities and challenges. In this context, the study of factors influencing policy-maker decisions to scale up health promotion interventions from small projects or controlled trials to wider state, national or international roll-out is increasingly important. This study aimed to: (i) examine the perspectives of senior researchers and policy-makers regarding concepts of ‘scaling up’ and ‘scalability’; (ii) generate an agreed definition of ‘scalability’ and (iii) identify intervention and research design factors perceived to increase the potential for interventions to be implemented on a more widespread basis or ‘scaled up’. A two-stage Delphi process with an expert panel of senior Australian public health intervention researchers (n = 7) and policy-makers (n = 7) and a review of relevant literature were conducted. Through this process ‘scalability’ was defined as: the ability of a health intervention shown to be efficacious on a small scale and or under controlled conditions to be expanded under real world conditions to reach a greater proportion of the eligible population, while retaining effectiveness. Results showed that in health promotion research insufficient attention is given to issues of effectiveness, reach and adoption; human, technical and organizational resources; costs; intervention delivery; contextual factors and appropriate evaluation approaches. If these issues were addressed in the funding, design and reporting of intervention research, it would advance the quality and usability of research for policy-makers and by doing so improve uptake and expansion of promising programs into practice.