Capillary blood glucose monitoring (BGM) has become an integral part of therapy for many persons with diabetes. The BGM data generated by patients and clinicians is used in the daily management of diabetes and in the clinical decisions involved in its treatment. This article provides a clinician's overview of the evolution and clinical use of BGM technology. In addition, the different types of diabetes are described, providing rationales for the various uses of BGM. Clinical decision making in acute-care and chronic-care settings is also described, with an emphasis on the maximal use of data and on quality assurance issues.