This chapter is devoted to time—one of the most important entities of objective mental reality. Time was originally conceptualized as a physical entity. However, upon phenomenological analysis, it comes across as a mental representation, an instrument—a mental coordinate axis that is vital for the constitution and measurement of another physical entity that is even accessible to perception, namely: the global and continuous change experienced by the world. Despite its mental nature, time is objective, independent of the individual, and measurable as it is an entity of objective mental reality. Thanks to the conceptualization of time and the distinct phenomenology of mental images (perception, memory, and imagination), the mind and objective mental reality have formed subjectively differentiated fragments of time—the past, the present, and the future. Without time, it would have been impossible to construct many derivative entities—such as development, process, history, century, year, minute, and so forth. These require not only the concept of time but also a representation of its flow, duration, and the comparison of temporal intervals that exist only in consciousness. After all, in the physical world there is only the present moment: the past is no longer here, and the future is yet to be. As a kind of central axis of objective mental reality, time structures not only objective mental reality itself but also culture and the history of society; therefore, differences in its conceptualization alter the way people from different societies understand the world. Time travel is not possible, since time itself is not a physical entity but a mental construction.