Within the field of healthcare the terms ' compliance' and 'non -compliance ' refer to the extent to which patients follow (or not) the regimens recommended by their doctors . An enormous amount of research over several decades has shown consist ently that between one third and one half of patients do not follow their doctors' advice and in particular fail to take the medicines prescribed for them ( Carter, Taylor & Levenson 2003; Donovan 1 995 ; Donovan & Blake 1 992; Haynes & Sackett 1 979; Sackett & Haynes 1 976; Stimson 1 974; Trostle 1 998 ) . The manifest failure of so many patients to act in their own best interests has baffled the medical establish ment. No distinctive characteristics of non-compliant individuals have been established, and the range of illnesses eliciting non-compliant behaviour runs across the spectrum from trivial to life-threatening. In one study Rovelli et al. found that patient non-compliance with immunosuppressive drugs following organ transplant caused a higher incidence of graft loss than uncontrollable rej ection affecting patients who had adhered to treatment as prescribed. Eighteen per cent of renal transplant patients were found to be non-compliant with treatment and the maj ority ( 9 1 % ) of these subsequently experienced either organ rej ection or death. The comparable failure rate for compliant patients was 1 8 % (Rovelli et al. 1 989 ) . The high rates of 'non-compliance' among AIDS patients have also been well established ( Chesney, Morin & Sherr 2002; Wright 2000 ) . Thousands of studies of non-compliance and how to modify patient behaviour have been conducted over the last three decades . However, this enormous effort has made no discernible impact on the consistently high rates of reported non-adherence . The mismatch between medical prescription and patient behaviour has persisted, and manifests itself in many different forms (Box 1 . 1 ) .