In computers, a printer driver or a print processor is a piece of software on a computer that converts the data to be printed to a format that a printer can understand. The purpose of printer drivers is to allow applications to do printing without being aware of the technical details of each printer model.

Printer drivers should not be confused with print spoolers, which queue print jobs and send them successively to a printer.

Unix and other Unix-like systems such as Linux and OS X use CUPS (short for Common Unix Printing System), a modular printing system for Unix-like computer operating systems, which allows a computer to act as a print server. A computer running CUPS is a host that can accept print jobs from client computers, process them, and send them to the appropriate printer. Printer drivers are typically implemented as filters. They are usually named the front end of the printing system, while the printer spoolers constitute the back end.

Backends are also used to determine the available devices. On startup, each backend is asked for a list of devices it supports, and any information that is available.

Users can use commands like, for example, "COPY file1 LPT1:" to print the content of a file to a printer. The contents is transferred to the printer without any interpretation. Therefore, this method of printing is either for files already stored in the corresponding printer's language or for generic text files without more than simple line-oriented formatting.

DOS also provides a dynamically loadable print spooler named PRINT as well as optional support to support screen captures also in graphics mode through GRAPHICS. If the optional character device driver PRINTER.SYS is loaded, DOS provides its code page switching support also for the associated printers—different types of dot matrix and ink jet printers are supported by default.

Beyond this, there are no system-wide printer-specific drivers for use at application level under MS-DOS/PC DOS. Under DR-DOS, however, the SCRIPT command can be loaded to run in the background in order to intercept and convert printer output from applications into PostScript to support PS-capable printers also by applications not supporting them directly.

On Microsoft Windows systems, printer drivers make use of GDI (Unidrv or PScript-based) or XPS (XPSDrv). Programs then use the same standard APIs to draw text and pictures both on screen and on paper. Printers which use GDI natively are commonly referred to as Winprinters and are considered incompatible with other operating systems, although there is software (such as PrintFil) which will make these printers work in a DOS prompt within Windows.

Win32 APIs also allow applications to send data directly to the spooler, bypassing the printer driver; however, few applications actually use this option.