Ever since the industrial revolution, people have tried in various ways to improve pruduction by machine tools. Most of these developments were from mechanical areas, in terms of making better (faster, more precise, with more options) machine tools, until the development of multi-axis machine tools. This was important because at the same time the products were changing, there was more complexity, and with a more complex product the programs bacame more complex as well, untill it was no longer possible to manually program these new, multi-axis machine tools. The next step in the development of production was the new way in which machine tools are being programmed, and that way is STEP-NC. In the first part of this paper it is mentioned the history and development of CNC machine tools, history of numerical control and programming history, and are briefly mentioned demands of today's market. This is followed by mentioning basics of CNC machine tools programming, programming methods, advantages and disadvantages of classical programming (G and M codes) and new programming method (STEP-NC). In the next part the cutter location data (CL data) and postprocessors are mentioned, as well as their role, i.e. shortcomings and why they are not used in STEP-NC. The main part of the paper deals with STEP and STEP-NC standards, their applications, and their role in today's machine tool production.