An eruv ([(ʔ)eˈʁuv]; Hebrew: עירוב, lit. 'mixture', also transliterated as eiruv or erub, plural: eruvin [(ʔ)eʁuˈvin] or eruvim) is a ritual halakhic enclosure made for the purpose of allowing activities which are normally prohibited on Shabbat (due to the prohibition of hotzaah mereshut lereshut), specifically: carrying objects from a private domain to a semi-public domain (carmelit), and transporting objects four cubits or more within a semi-public domain. The enclosure is made within some Jewish communities, especially Orthodox Jewish communities.

An eruv accomplishes this by symbolically integrating a number of private properties and spaces such as streets and sidewalks into one larger "private domain" by surrounding it with mechitzas, thereby avoiding restrictions of transferring between domains. Often a group constructing an eruv obtains a lease to the required land from a local government.

An eruv allows Jews to carry, among other things, house keys, tissues, medication, or babies with them, and to use strollers and canes. The presence or absence of an eruv thus especially affects the lives of strictly observant Jews with limited mobility and those responsible for taking care of babies and young children.