Common Internet File System (CIFS) is a protocol that lets programmes make requests for files and services on remote computers on the Internet. CIFS uses the client/server programming model. A client programme makes a request of a server programme (usually in another computer) for access to a file or to pass a message to a programme that runs in the server computer. The server takes the requested action and returns a response.

CIFS is a public or open variation of the Server Message Block Protocol developed and used by Microsoft. Like the SMB protocol, CIFS runs at a higher level than and uses the Internet's TCP/IP protocol. CIFS is viewed as a complement to the existing Internet application protocols such as the File Transfer Protocol (FTP) and the Hypertext Transfer Protocol (HTTP).