Many factors are contributing to any increased awareness of and interest in computer security. This article has described two aspects of computer security, identification of users and cryptography as a tool for data security. We looked at a number of ways to verify the identity of a user, including things a person knows, has, or is. Combinations of techniques were considered as a means of increasing security. Next, we looked at some simple examples of cryptosystems, including the rail fence cipher (a transposition technique), and the Caesar cipher (a substitution technique). Two computer systems were described, DES (a product cipher), and RSA (a cipher based on exponentiation and the mod operation).