An aperture card is a punched card with a cut-out window into which a chip of microfilm is mounted. The card is typically punched with machine-readable metadata associated with the microfilm image, and printed across the top of the card for visual identification.

Aperture cards are used for archiving, for making multiple inexpensive copies of a document for ease of distribution, and for engineering drawings.

Machinery exists to automatically store, retrieve, sort, duplicate, create, and digitize cards with a high level of automation. Aperture cards can be converted to digital documents using scanning equipment and software.

An aperture card is a type of punched card with a cut-out window into which a chip of microfilm is mounted. The card is typically punched with machine-readable metadata associated with the microfilm image, and printed across the top of the card for visual identification; it may also be punched by hand in the form of an edge-notched card. Information about the drawing, for example the drawing number, could be both punched and printed on the remainder of the card. With the proper machinery, this allows for automated handling. In the absence of such machinery, the cards can still be read by a human with a lens and a light source.

The microfilm chip is most commonly 35 mm in height, and contains an optically reduced image, usually of some type of reference document, such as an engineering drawing, that is the focus of the archiving process.

Aperture cards are used for archiving or for making multiple inexpensive copies of a document for ease of distribution. They are used for engineering drawings from all engineering disciplines. The U.S. Department of Defense once made extensive use of aperture cards, and some are still in use, but most data is now digital.

Aperture cards have, for archival purposes, some advantages over digital systems. They have a 500-year lifetime, they are human readable, and there is no expense or risk in converting from one digital format to the next when computer systems become obsolete.

Aperture cards require a filing system, as well as experienced clerks and often sorting equipment. In order for records on aperture cards to be useful, they need to be archived correctly. Cards need to be archived either via a numbering scheme (in which each card is assigned a number and sorted according to the number) or a index system (in which cards are sorted by metadata). As with paper records, the indexing, locating, and refiling processes add significantly to the workload of record keepers. As is common with other forms of record keeping, misfiling cards after use (particularly in large archives) results in the card being lost. It may take significant time and effort from an archivist to locate a lost record.