We are delighted to welcome the attendees of the Fourth International Wo- shop on Digital Watermarking (IWDW). Watermarking continues to generate strong academic interest. Commercialization of the technology is proceeding at a steadypace. We haveseen watermarkingadoptedfor DVD audio.Fingerpri- ing technology was successfully used to determine the source of pirated video material. Furthermore, a number of companies are using watermarking as an enabling technology for broadcast monitoring services. Watermarking of digital cinema contentis anticipated. Future applications may also come from areas- related to digital rights management. For example, the use of watermarking to enhance legacy broadcast and communication systems is now being considered. IWDW 2005 offers an opportunity to reffect upon the state of the art in digital watermarking as well as discuss directions for future research and applications. This year we accepted 31 papers from 74 submissions. This 42% acceptance rate indicates our commitment to ensuring a very high quality conference. We thank the members of the Technical Program Committee for making this possible by their timely and insightful reviews. Thanks to their hard work this is the first IWDW at which the final proceedings are available to the participants at the time of the workshop as a Springer LNCS publication.