Multimorbidity, or co-occurrence of several chronic diseases, is of increasing importance for health professionals and the organization of the health care system. It is important for patients, particularly in relation to quality of life and functional status, for family practitioners in relation to support and coordination skills and for the health system in relation to costs and organization. In this article we introduce the concepts of chronic conditions, multimorbidity and its impact (burden) on the patient and the family practitioner, the importance of a prioritization of care and of the patient's health skills (health literacy), the consequences of polypharmacy and the importance of a network of health professionals. These themes will be developed throughout this issue.