A computer file is a collection of data on a computer storage device, primarily identified by its filename. Just as words can be written on paper, so too can data be written to a computer file. Files can be shared with and transferred between computers and mobile devices via removable media, networks, or the Internet.

Different types of computer files are designed for different purposes. A file may be designed to store a written message, a document, a spreadsheet, an image, a video, a program, or any wide variety of other kinds of data. Certain files can store multiple data types at once.

By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and copied an arbitrary number of times.

Files are typically organized in a file system, which tracks file locations on the disk and enables user access.

The word "file" derives from the Latin filum ("a thread, string").

"File" was used in the context of computer storage as early as January 1940. In Punched Card Methods in Scientific Computation, W. J. Eckert stated, "The first extensive use of the early Hollerith Tabulator in astronomy was made by Comrie. He used it for building a table from successive differences, and for adding large numbers of harmonic terms". "Tables of functions are constructed from their differences with great efficiency, either as printed tables or as a file of punched cards."

In February 1950, in a Radio Corporation of America (RCA) advertisement in Popular Science magazine describing a new "memory" vacuum tube it had developed, RCA stated: "the results of countless computations can be kept 'on file' and taken out again. Such a 'file' now exists in a 'memory' tube developed at RCA Laboratories. Electronically it retains figures fed into calculating machines, holds them in storage while it memorizes new ones – speeds intelligent solutions through mazes of mathematics."

In 1952, "file" denoted, among other things, information stored on punched cards.