This guide reviews what is known about educational and clinical supervision practice through a literature review and a questionnaire survey. It identifies the need for a definition and for explicit guidelines on supervision. There is strong evidence that, whilst supervision is considered to be both important and effective, practice is highly variable. In some cases, there is inadequate coverage and frequency of supervision activities. There is particular concern about lack of supervision for emergency and 'out of hours work', failure to formally address under-performance, lack of commitment to supervision and finding sufficient time for supervision. There is a need for an effective system to address both poor performance and inadequate supervision. Supervision is defined, in this guide as: 'The provision of guidance and feedback on matters of personal, professional and educational development in the context of a trainee's experience of providing safe and appropriate patient care.' A framework for effective supervision is provided: (1) Effective supervision should be offered in context; supervisors must be aware of local postgraduate training bodies' and institutions' requirements; (2) Direct supervision with trainee and supervisor working together and observing each other positively affects patient outcome and trainee development; (3) Constructive feedback is essential and should be frequent; (4) Supervision should be structured and there should be regular timetabled meetings. The content of supervision meetings should be agreed and learning objectives determined at the beginning of the supervisory relationship. Supervision contracts can be useful tools and should include detail regarding frequency, duration and content of supervision; appraisal and assessment; learning objectives and any specific requirements; (5) Supervision should include clinical management; teaching and research; management and administration; pastoral care; interpersonal skills; personal development; reflection; (6) The quality of the supervisory relationship strongly affects the effectiveness of supervision. Specific aspects include continuity over time in the supervisory relationship, that the supervisees control the product of supervision (there is some suggestion that supervision is only effective when this is the case) and that there is some reflection by both participants. The relationship is partly influenced by the supervisor's commitment to teaching as well as both the attitudes and commitment of supervisor and trainee; (7) Training for supervisors needs to include some of the following: understanding teaching; assessment; counselling skills; appraisal; feedback; careers advice; interpersonal skills. Supervisors (and trainees) need to understand that: (1) helpful supervisory behaviours include giving direct guidance on clinical work, linking theory and practice, engaging in joint problem-solving and offering feedback, reassurance and providing role models; (2) ineffective supervisory behaviours include rigidity; low empathy; failure to offer support; failure to follow supervisees' concerns; not teaching; being indirect and intolerant and emphasizing evaluation and negative aspects; (3) in addition to supervisory skills, effective supervisors need to have good interpersonal skills, good teaching skills and be clinically competent and knowledgeable.