Bruce Schneier (born January 15, 1963, pronounced /ˈʃnаɪər/) is an American cryptographer, computer security specialist, and writer. He is the author of several books on computer security and cryptography, and is the founder and chief technology officer of BT Counterpane, formerly Counterpane Internet Security, Inc.

Originally from New York City, Schneier currently lives in Minneapolis, Minnesota. Schneier has a Master's degree in computer science from American University and a Bachelor of Science degree in physics from the University of Rochester. Before Counterpane, he worked at the United States Department of Defense and then AT&T Bell Labs. In August 1999, Schneier founded Counterpane Internet Security. Counterpane was acquired by BT in October 2006, and is now known as BT Managed Security Solutions. Schneier is currently the Chief Security Technology Officer of BT.

Schneier's Applied Cryptography is a popular reference work for cryptography. Schneier has designed or co-designed several cryptographic algorithms, including the Blowfish, Twofish and MacGuffin block ciphers, the Helix and Phelix stream ciphers, and the Yarrow and Fortuna cryptographically secure pseudo-random number generators. Solitaire is a cryptographic algorithm developed by Schneier for use by people without access to a computer, called Pontifex in Neal Stephenson's novel Cryptonomicon. In October 2008, Schneier, together with seven others, introduced the Skein hash function family, which has been submitted to the NIST hash function competition.