Behavioural interventions are a technique used by social scientists and health professionals to mediate the behaviour of a subject. Traditionally, interventions take the form of tailored advice given in a face-to-face setting. Internet-based behavioural interventions harness the power of the web to deliver tailored advice to participants at the time that most suits them. The LifeGuide project is a multidisciplinary collaboration with the aim of developing and proving a set of software tools for the development and deployment of internet-based behavioural interventions. The tools developed in LifeGuide cover the complete lifecycle of an intervention, from initial authoring to trialling and refinement to final deployment. Looking ahead, in the longer term we intend to investigate how the LifeGuide toolset can be applied to other domains.