Abstract: File transfer is the movement of digital information from one data terminal to another. This digital information is organized into characters, frames and files. File transfer applications typically demand a very high level of reliability, unlike voice application, a single erroneous bit can render a multi megabyte file useless to the end user. Communication links in wireless and wired file transfer systems are designed to be highly reliable. The error control systems for these applications use error detection coupled with retransmission requests to maximize reliability at some cost to throughput. At there simplest, such error control systems use parity-check bits or CRC codes to trigger retransmission requests. Since the retransmission requests occur well below the application layer and such protocols are called Automatic Repeat Request (ARQ) protocols. More complicated protocol includes elements of FEC and packet combining to reduce the frequency of retransmission requests. In this article parity, CRC and pure ARQ protocols are discussed. Several popular file transfer protocols are provided as examples. Consideration is then given to hybrid protocols and packet combining.