Published in Journal of Medical Internet Research, this viewpoint article co-authored by IBTN Founding Member Dr. S. Michie shares recommendations coming out of a two-day international workshop on how to create, evaluate, and implement effective digital interventions in relation to health behaviours. It makes distinctions between sustained, effective and sufficient patient engagement, and recognizes the potential of digital interventions for testing and advancing theories of behaviour change by generating ecologically valid, real-time objective data.