The work provides a comprehensive overview of the diverse natural and social science aspects of modern time research, along with an in-depth presentation of time concepts and timekeeping systems from numerous cultures throughout all epochs of human history. This broad representation allows for a holistic view of the whole and its development. Embedded within the natural time scales is human time, individual perceptions of time, and socially determined concepts of time. These are reflected in language, in the measurement of time, and in timekeeping systems. The processes that led to the formation of differentiated time concepts at various cultural levels, and consequently to a variety of calendars, are examined in detail. Magically-ritual or religiously motivated festivals play a significant role in this context.