What is an Eruv and what is its purpose? I have heard many different reasons.

The word Eruv means “a combination.” One can have an Eruv of three types:

1) Eruv Chatzeiros or “Combination of Courtyards” – On the Sabbath there is a prohibition to carry items in a public domain or to transfer them from a public domain to a private domain. Within a private domain, like inside one’s home, carrying items is permitted. An Eruv can combine different private domains and semi-public domains to form one large private domain allowing items to be carried throughout the enlarged domain. This is accomplished by having all residents of the area contribute to a selection of food and keeping the food in one of the residencies. If these residencies are not one enclosed area already it is necessary to construct walls, or fences, around the entire area. If you’ve heard of an entire community being surrounded by an Eruv it is one of this type. They surround the community with a string attached to a series of poles to form a fence. Often the telephone poles and wires are used as part of the fence. This Eruv essentially makes the entire community one private domain. The laws involved in constructing this type of Eruv are highly complex, so communities who desire such an Eruv to permit the carrying of items on the Sabbath are advised to work with a Rabbi who is an expert in this field of Jewish Law.

2) Eruv Techumin or “Combination of Boundaries” – On the Sabbath there is a prohibition to travel a set distance beyond the radius of the city limits. By means of an Eruv one extends this distance in a particular direction by placing some food in an area near the end of the city limits. When this food is placed Jewish Law considers the person to have taken up residency in this new location and thereby the radius of distance one can travel on the Sabbath is moved. The laws for this Eruv are not as complex as the Eruv Chatzeiros above, but one should still consult their Rabbi for the proper steps to take.

3) Eruv Tavshilin or “Combination of Cook Foods” – There is a prohibition to prepare anything on the Holiday for the Sabbath. Only tasks needed for the day itself are allowed. Because of this, when a Holiday occurs on a Friday one cannot prepare anything for the following Sabbath without making an Eruv. The Eruv consists of a loaf of bread or a Matzah, plus a cooked item – customarily a hard-boiled egg. By preparing it one combines the Sabbath preparation with Friday’s Holiday tasks. It is customary to eat this Eruv on the Sabbath as part of the Sabbath meal.

The above explanation is highly simplified, but it should give you a feel
for this intricate topic.

Best Regards,
Rabbi Mordechai Dixler