In the digital environment, steganography has increasingly received attention over the last decade. Steganography, which literally means “covered writing,” includes any process that conceals data or information within other data or conceals the fact that a message is being sent. Though the focus on use of steganography for criminal and terrorist purposes detracts from the potential use for legitimate purposes, the focus in this chapter is on its role as a security threat. The history of stenography as a tool for covert purposes is addressed. Recent technical innovations in computerized steganography are presented, and selected widely available steganography tools are presented. Finally, a brief discussion of the role of steganalysis is presented.