This book discusses the structure and design of the Rijndael cipher, the underlying mathematics, attack strategies and implementation specifics (across a range of platforms).
Most of the material in the book can be found from the many papers on Rijndael, including both authors' PhD theses, yet its compilation here is more than the sum of its parts. The book is very well written and integrated, and a joy to read.
The authors have two groups of people in mind - implementers and academics. Academics are better served by this book, since the majority of pages 80 to 209 contain lots of pretty mathematics to underpin deep thought. Still the specification of Rijndael is unambigious and easy to read, and the book contains reference code (which looks *really* slow, as reference code should :-).
For me, I'm glad I bought the book just because of the excellent and up-to-date bibliography.