Fast Software Encryption2009wasthe16thin a seriesofworkshopsonsymm- ric key cryptography. Starting from 2002, it is sponsored by the International Association for Cryptologic Research (IACR). FSE 2009 was held in Leuven, Belgium, after previous venues held in Cambridge, UK (1993, 1996), Leuven, Belgium (1994, 2002), Haifa, Israel (1997), Paris, France (1998, 2005), Rome, Italy (1999), New York, USA (2000), Yokohama, Japan (2001), Lund, Sweden (2003), New Delhi, India (2004), Graz, Austria (2006), Luxembourg, Lux- bourg (2007), and Lausanne, Switzerland (2008). The workshop’s main topic is symmetric key cryptography, including the designoffast andsecuresymmetrickeyprimitives, suchas block ciphers, stream ciphers, hash functions, message authentication codes, modes of operation and iteration, as well as the theoretical foundations of these primitives. This year, 76 papers were submitted to FSE including a large portion of papers on hash functions, following the NIST SHA-3 competition, whose wo- shop was held just after FSE in the same location. From the 76 papers, 24 were accepted for presentation. It is my pleasure to thank all the authors of all s- missions for the high-quality research, which is the base for the scienti?c value of the workshop. The review process was thorough (each submission received the attention of at least three reviewers), and at the end, besides the accepted papers, the Committee decided that the merits of the paper "Blockcipher-Based Hashing Revisited" entitled the authors to receive the best paper award. I wish to thank all Committee members and the referees for their hard and dedicated work.