Index Card

An index card (or system card in Australian English) consists of heavy paper stock cut to a standard size, used for recording and storing small amounts of discrete data. It was invented by Carl Linnaeus, around 1760.

The most common size for index cards in North America and Russia is 3 by 5 inches (76.2 by 127.0 mm), hence the common name 3-by-5 card. Other sizes widely available include 4 by 6 inches (101.6 by 152.4 mm), 5 by 8 inches (127.0 by 203.2 mm) and ISO-size A7 (74 by 105 mm/2.9 by 4.1 in). Cards are available in blank, ruled and grid styles in a variety of colors. Special divider cards with protruding tabs and a variety of cases and trays to hold the cards are also sold by stationers and office product companies. They are part of standard stationery and office supplies in the United States, but in other countries, such as China, are not.

Index cards are used for a wide range of applications and environments: in the home to record and store recipes, shopping lists, contact information and other organizational data; in business to record presentation notes, project research and notes and contact information; in schools as flash cards or other visual aids; and in academic research to hold data such as bibliographical citations or notes. An often-suggested organization method is to use the smaller 3-inch by 5-inch cards to record the title and citation information of works cited, while using larger cards for recording quotes or other data. Index cards are used for many events and are very helpful for planning.

Until the conversion of library catalogs beginning in the 1980s, the primary tool used to locate books was the card catalog in which every book was filed with three cards, filed alphabetically under its title, author and subject (if non-fiction). Similar catalogs were used by law firms and other organizations to organize large quantities of stored documents. However, the adoption of standard cataloging protocols throughout nations with international agreements, along with the rise of the Internet and the conversion of cataloging systems to digital storage and retrieval, have made widespread use of index cards for cataloging purposes obsolete.