Diabetes mellitus is a disease that affects a large number of people around the world. There are no effective methods to completely cure diabetes, and patients have to constantly monitor their blood sugar levels, so there is still a need for improved sensors. In addition to diabetes, quantitative values of glucose levels affect the development of some endocrine diseases and problems with nervous tissue. In this review, we will describe existing developments, the principles of glucose measurement, sensor designs, the materials they are made of, and how nanotechnology is improving the sensors under development by increasing sensitivity and surface area and improving catalytic properties.