This book constitutes the thoroughly refereed post-proceedings of the7th International Workshop on Information Hiding, IH 2005, held in Barcelona, Spain in June 2005.The 28 revised full papers presented together with an invited talk werecarefully selected from 90 papers submitted. The papers are organized in topical sections on anonymity, watermarking, theory, watermark attacks, steganography, hiding in unusual content, steganalysis, software watermarking, and fingerprinting.