An eruv is a ritual halakhic enclosure made for the purpose of allowing activities that are normally prohibited on Shabbat, specifically carrying objects from a private domain to a semi-public domain, and transporting objects four cubits or more. The term eruv is a shortening of eruv chatzerot, which means "merger of . An eruv allows Jews to carry items such as house keys, tissues, medication, or babies with them, and to use strollers and canes, which are otherwise forbidden from being carried outside one’s home during Shabbat, in the absence of an eruv.

An eruv is a symbolic demarcation of the private sphere, one that communities come together to create. It is not a physical wall or border, but rather a boundary that allows observant Jews to carry needed things in public on Shabbat. An eruv can be comprised of a series of pre-existing structures such as walls, fences, electrical poles, and wires, and/or structures created expressly for the eruv, often a wire mounted on poles.

In Israel, almost every Jewish community is enclosed by an eruv, and outside Israel, there are over 150 community eruvin, as well as thousands of private ones enclosing only a few homes or linking a synagogue to one or more nearby homes. Most major cities in North America have at least one, often surrounding only the Orthodox Jewish neighborhoods rather than the entire city. For example, Manhattans eruv is a thin fishing line above the skyline that encircles the island, attached to posts around the perimeter of the city, from First Street to 126th.

The concept of the eruv was first established almost 2,000 years ago to allow Jews to more realistically follow the laws of Sabbath rest, particularly one — no carrying on the Sabbath. The eruv helps enhance an aspect of Shabbat that the Rabbis considered vital — “oneg Shabbat,” the injunction to enjoy the Sabbath. With an eruv, Shabbat events are available to all families, and individuals are able to carry house keys, reading glasses, or books outside their homes.