The design system is an integral part of the work of a graphical user interface and user experience designer whose job is to create digital products from scratch or improve existing products. Its function is to reduce the number of iterations in the work process and to reduce the time required to produce components that have already been used. For this reason, the designers have developed a unique library from which frequently used components can be retrieved. The basic function of the design system is to speed up the work process. When components are arranged in a certain way, are properly named, and can be customised as needed, they leave room for the designer to focus on the user experience. The need for a design system is not the same for every project. On smaller-scale projects, the design system is not as important, while on larger-scale projects it is often maintained by a separate team. To better understand its role, it is necessary to explain the entire work process. The creation of the design system comes after the research phase and may continue throughout the duration of the project. This paper defines the work phases of UX /UI designers, focusing on the design system phase. Since UX /UI Design is a profession that is still evolving, there are several interesting practices, tools and work areas in this profession. The goal is to describe this profession as best as possible and make a statement about what a design system encompasses and how it is used. The paper is a kind of inventory and comparison of existing practices around the world.