Signcryption is a new paradigm in public key cryptography that simultaneously fulfills both the functions of digital signature and public key encryption in a logically single step, and with a cost significantly lower than that required by the traditional "signature followed by encryption" approach. This paper summarizes currently known construction methods for signcryption, carries out a comprehensive comparison between signcryption and "signature followed by encryption", and suggests a number of applications of signcryption in the search of efficient security solutions based on public key cryptography. Keywords Authentication, Digital Signature, Encryption, Key Distribution, Secure Message Delivery/Storage, Public Key Cryptography, Security, Signcryption.