 What is time, and is it real? If it is, does time flow or lapse or pass? Are the future or the past as real as the present? These metaphysical questions have been debated for more than two millennia, with no resolution in sight. Modern physics provides us, however, with tools that enable us to sharpen these old questions and generate new arguments. Does the special theory of relativity, for example, show that there is no temporal passage or that the future is as real as the present? The focus of this entry will be on these new insights into those old questions.