The work of a master, Relativity, the Special and the General Theory: A Popular Exposition, Volume One is Albert Einstein's own attempt to present his theories of relativity to non-physicists.
The book is composed of three parts. Part one presents the Special Theory of Relativity and the intimate connection of space and time (spacetime, or "ST"). Part two highlights the General Theory of Relativity, in which Einstein argues that space and time are not absolute and are modified by gravitational forces. In part three, Einstein applies these theories to a consideration of the universe as a whole, with specific discussion about Newton's Law and a sketch of the structure of space according to the General Theory of Relativity. The book frequently refers to an analogy involving a man on a train and a man on and embankment, to which Einstein applies his theories to present varying outcomes. These analogies greatly enhance the layperson's understanding.
Einstein's stated goal in Relativity, the Special and the General Theory was to "present the ideas in the simplest and most intelligible form," and in this regard he was largely successful. One does not need to have an understanding of the mathematical principles of theoretical physics in order to read this book. However, that is not to say this book is not a challenging read. The layman will likely find some of the passages quite dense, and the mathematical calculations that are presented may be difficult to follow. While this will not greatly impact one's surface level understanding of Einstein's theories, one's ability to fully grasp the theories presented will depend on their scientific and mathematical background.
Relativity, the Special and the General Theory is highly recommended. It is an important work by one of the world's great thinkers, and it presents complex theories in an accessible manner. This book is a worthy addition to anybody's library.