The beginning of the 21st century saw the arrival of continuous glucose monitoring systems (CGMS). For over a decade they were seen as an excellent tool providing data on the daily glucose profile patterns in patients with diabetes, but confined to research. Over 20 years ago hardly anyone expected CGMS to become an extremely useful device in everyday life with diabetes as the cost, the burdensome design and accuracy were at the time the main concerns. However, in the last few years CGMS has become available to the entire diabetic population, and it is affordable to many of them. During this time, the technology developed immensely, and patients can now use reliable systems to give them instant, online insight into their blood glucose excursions 24/7. Moreover, the accumulated evidence indicates that arming patients with knowledge of their current glucose value and the trends of its variability translates into significant improvement in overall glucose management. The patients who benefit most, as research data and clinical experience show, are those who are treated with insulin, in particular individuals with type 1 diabetes. Progress in glucose monitoring – the journey from measuring urine glucose through portable glucose meters to CGMS – has also changed the metrics that are used to assess metabolic control of diabetes. In recent years the concept of time in range (TIR) has been introduced, which is now being widely adopted into clinical guidelines and practice. In 2021 the use of real-time CMGS in patients with type 1 diabetes was recommended by the American Diabetes Association (ADA) and European Association for the Study of Diabetes (EASD) as a main tool for self-monitoring of blood glucose. The article is a state-of-the-art review presenting current evidence-based knowledge and views on the practical use of CGMS in this group of patients, with clinical implications and opportunities discussed in detail.