The digital revolution has brought about profound changes in our society and our lives. This book discusses the issues regarding multimedia data hiding and its application to multimedia security and communication, addressing both theoretical and practical aspects and tackling both design and attack problems. The book is organized into three parts. In the fundamental issues part, a few key elements of data hiding are identified through a layered structure; data hiding is modeled as a communication problem where the embedded data is the signal to be transmitted. A comprehensive solution is proposed that addresses considerations for choosing constant- or variable embedding rate and enhancing performance in each case. Algorithm and system designs are presented in the second part for binary images, grayscale and color images, and videos. The designs provide concrete examples, such as annotation, tamper detection, copy/access control, fingerprinting, and ownership protection. Finally, in the third part, attacks and countermeasures for both known and unknown data-hiding algorithms are considered, respectively, for problems surrounding digital watermarking and digital music.