For a general audience with little to no physics background:
* "A Brief History of Time" by Stephen Hawking: While not solely focused on relativity, it provides a highly accessible introduction to the concepts and their implications. It's famous for its readability but simplifies some details.
* "Cosmos" by Carl Sagan: Similar to Hawking's book, it's a broader exploration of science but includes engaging chapters on relativity and its context within the universe.
* "Einstein's Cosmos: How Albert Einstein's Vision Transformed Our Understanding of Space and Time" by Michio Kaku: Kaku presents Einstein's theories in a clear and compelling narrative, focusing on their historical context and philosophical implications.
For a more rigorous introduction with some physics background (college-level math helpful but not strictly required):
* "Spacetime Physics" by Edwin F. Taylor and John A. Wheeler: This is a classic textbook that excels at building intuition for special relativity using thought experiments and clear explanations. It requires some mathematical maturity but avoids overly complex formalism.
* "Relativity: The Special and General Theory" by Albert Einstein: Einstein's own exposition. It's accessible to a motivated reader with some math background, but its style can be challenging at times. It's historically important and offers unique insight directly from the source.
For a mathematically rigorous treatment (requires significant physics and mathematics background, including calculus and vector calculus):
* "Gravitation" by Charles W. Misner, Kip S. Thorne, and John Archibald Wheeler (MTW): This is a monumental, comprehensive, and incredibly detailed textbook often used in graduate-level courses. It's not for the faint of heart but is considered the definitive reference.
* "Introduction to General Relativity" by L.D. Landau and E.M. Lifshitz: Another classic and rigorous text known for its clarity and conciseness, though still challenging.
In summary:
* Beginner: Hawking, Sagan, or Kaku.
* Intermediate: Taylor & Wheeler, or Einstein's own book.
* Advanced: MTW or Landau & Lifshitz.
Before choosing, consider your mathematical background and desired level of detail. If you're unsure, starting with a more accessible book like Taylor & Wheeler or one of the general audience books is a good strategy. You can then progress to more advanced texts as your understanding grows.