This book constitutes the thoroughly refereed post-workshop proceedings of the Third International Workshop on Information Hiding, IH'99, held in Dresden, Germany, in September/October 1999. The 33 revised full papers presented were carefully reviewed and selected from a total of 68 submissions. The dominating topic, dealt with in various contexts, is watermarking. The papers are organized in sections on fundamentals of steganography, paradigms and examples, beyond symmetric steganography; watermarking: proving ownership, detection and decoding, embedding techniques, new designs and applications, improving robustness, software protection; separating private and public information; and stego-engineering.