Medicines are the most common evidence-based healthcare intervention. However, low levels of patient adherence to medicines for chronic illnesses mean that some expenditure may be wasted. This article provides a guide for nurses who wish to explore the patient adherence literature and improve clinical practice. The related terms of compliance, adherence and concordance are defined, and differences in interpretation are explained. Broad roles are suggested for nurses who administer or prescribe medicines, and levels of patient adherence to various cardiovascular medicines are discussed. The risks and benefits associated with higher levels of adherence are summarized, and patient views about adherence are illustrated. Finally, some practical strategies for improving patient adherence and engagement in decision making are evaluated.