Time is considered as an independent entity which cannot be reduced to the concept of matter, space or field. The point of discussion in this book is the "time flow" conception due to N.A. Kozyrev (1908-1983), a Russian astronomer and natural scientist. In addition to a review of the experimental studies of "the active properties of time", by both Kozyrev's and modern ones, the book contains different interpretations of Kozyrev's views and some developments of his ideas in the fields of geophysics, astrophysics, general relativity and theoretical mechanics.