The way that people communicate, consume media and seek and receive information is changing. Forty per cent of the world's population now has an internet connection, the average global social media penetration is 39 % and 1·5 billion people have internet access via mobile phone. This large-scale move in population use of digital, social and mobile media presents an unprecedented opportunity to connect with individuals on issues concerning health. The present paper aims to investigate these opportunities in relation to dietary behaviour change. Several aspects of the digital environment could support behaviour change efforts, including reach, engagement, research, segmentation, accessibility and potential to build credibility, trust, collaboration and advocacy. There are opportunities to influence behaviour online using similar techniques to traditional health promotion programmes; to positively affect health-related knowledge, skills and self-efficacy. The abundance of data on citizens' digital behaviours, whether through search behaviour, global positioning system tracking, or via demographics and interests captured through social media profiles, offer exciting opportunities for effectively targeting relevant health messages. The digital environment presents great possibilities but also great challenges. Digital communication is uncontrolled, multi-way and co-created and concerns remain in relation to inequalities, privacy, misinformation and lack of evaluation. Although web-based, social-media-based and mobile-based studies tend to show positive results for dietary behaviour change, methodologies have yet to be developed that go beyond basic evaluation criteria and move towards true measures of behaviour change. Novel approaches are necessary both in the digital promotion of behaviour change and in its measurement.Social media: Digital communications: Behaviour change: Health communications:Mobile healthThe way that people communicate with each other, consume media and seek and receive information has changed dramatically. Newspaper readership is falling, radio listenership fragmenting (2) and people time shift their television viewing, skipping advertising (3) . Forty per cent of the world's population now has an internet connection compared with <1 % in 1995. This number is set to reach 43 % (3 billion) by the end of 2014 (4) . Average global social media penetration is 39 %, ranging from 82 % in Canada to 12 % in India (5) . One and a halfbillion people have relatively fast access to the internet from their mobile phone (5) . This large-scale move in population use of digital, social and mobile media presents an unprecedented opportunity to connect with individuals on issues concerning health and behaviour change and to weave health information into the daily lives of citizens. The present paper aims to investigate this in relation to dietary behaviour change, drawing on examples from both nutrition and food safety. It includes an exploration of the scientific and grey literature and relevant websites, comb...