Electronic Article Surveillance (EAS) is a technological method for preventing shoplifting from retail stores or pilferage of books from libraries. Special tags are fixed to merchandise or books.

These tags are removed or deactivated by the clerks when the item is properly bought or checked out. At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses active tags. For high-value goods that are to be manipulated by the patrons, wired alarm clips may also be used; these, being less common and technologically less mysterious, are not covered by this article.

There are several types of EAS systems. In each case, the EAS tag or label is affixed to an item. The tag is then deactivated when the item is purchased (or legally borrowed) at the checkout desk. When the item is moved through the gates (usually at a door to the premises), the gate is able to sense if the tag is active or deactivated and sound an alarm if necessary.

EAS systems are used anywhere there is a chance of theft from small items to large. By placing an EAS tag on an item, it is not necessary to hide the item behind locked doors and so makes it easier for the consumer to review the product. Today's EAS source tagging, where the tag is built into the product at the point of manufacture or packaging, has become commonplace. This makes the labeling of goods unnecessary, saving time and money at the store.