Working time is an important institute of labor law and has been at it‵s center since the very beginning of the development of that law. Also, it is an institute that is close to all workers, since it is a period in which workers exercise their right to work and earn income, and outside of which they rest. The concept of working time, both in croatian and european law, includes three specific constitutive elements that must exist in order for a certain period of time to be qualified as working time, while otherwise it will be considered rest period. The concept of working time also includes on-call time during which workers do not work effectively, but are obliged to be at the workplace and perform job duties immediately as soon as the need arises. On the other hand, stand-by time, during which workers are not obliged to be at the workplace but to be available for the employer and respond to his call to perform work, does not constitute working time. Exceptionally, stand-by time can constitute working time if the constraints imposed on the worker are very intense and therefore, prevent real rest. After all, working time is an essential means of health and safety protection of workers, where the provisions on the limitation of weekly working time as well as the provisions on te minimum rest periods are highlighted.