Guidelines are important tools to improve knowledge management, processes and outcomes in health care. Their function is to assist professionals and patients decisions about appropriate and effective practice, especially in those areas of health care where considerable variation or potential for improvement exists. The achievement of a favourable impact necessitates both a systematic and methodically sound approach in the development of guidelines. The German Instrument for Methodological Guideline Appraisal, an adopted and supplemented version of the AGREE (Appraisal of Guidelines Research and Evaluation) instrument, provides 34 quality criteria guideline developers should take into account. However, the impact of guidelines is not only determined by methodological soundness but also by the choice of the guideline topic (need for a guideline), by its dissemination (accessibility) and implementation (acceptance and use). Finally, this impact must be monitored by means of guideline-based quality indicators.