The book "Information Hiding" presents the proceedings of the ninth edition of the conference of the same name, which took place from June 11 to 13, 2007, in Saint Malo, France. This conference has established itself as a significant forum for the discussion and exchange of ideas in the field of information hiding. This volume documents the results of 105 submitted papers from 25 countries, representing the highest number of submissions in the history of the conference. The selection of contributions was a challenging task, as only 25 papers were accepted for presentation. This underscores the high quality and relevance of the topics addressed. In addition to traditional areas such as watermarking and steganography, new topics like the application of Tardos codes for fingerprinting and digital forensics were also covered. The careful review of the submitted papers by at least three reviewers per contribution ensures the scientific integrity and high standard of the conference.