What are the best relativity books available for understanding the theory of relativity?

Some of the best books for understanding the theory of relativity include "Relativity: The Special and General Theory" by Albert Einstein, "The Elegant Universe" by Brian Greene, and "Black Holes and Time Warps" by Kip Thorne. These books provide clear explanations of the concepts of relativity and are accessible to readers at a 12th-grade level.