Blood glucose control is central to the very nature of diabetes, and the late complications which can develop. Unfortunately, it cannot be sensed by the person with diabetes unless levels are very high or very low. Accordingly, blood glucose control has to be measured reliably, and this needs to be done in the clinic and in normal life. Evidently, the results have then to be related to the risks of developing complications – hence targets and intervention levels. Here we summarize three chapters from the Global Guideline that deal with ways of measuring blood glucose control, and interpreting the results of such measurements.