Clinical guidelines play an important supportive role in improving everyday clinical practice. Their benefits are beyond doubt because failure to implement them is associated with a poorer prognosis. Nevertheless, clinical guidelines have their critics and limitations. Simply publishing guidelines does not mean that they will be implemented. It is essential, therefore, to understand the difficulties that can impede implementation in practice. Both the assessment of guideline implementation and the design of programs for improving implementation require a specific methodology. Use of this methodology to devise programs that encourage the implementation of clinical guidelines has resulted in improved adherence to guideline recommendations and, significantly, in a reduction in morbidity and mortality.