A.The mitzva

1.Midaraisa, biblically, it is permissible to cook on Yom Tov for Shabbos(1). Therefore if Yom Tov falls out on Thursday and/or Friday, all Shabbos preparations may be performed in their usual manner. The Sages however, were afraid that if on Yom Tov it were permissible to cook for Shabbos, some might infer that all cooking is permissible, even for a week day meal. Therefore Chazal instituted the making of an Eruv Tavshilin. The Eruv Tavshilin made on Erev Yom Tov is in essence, the beginning of the Shabbos preparations. When we then go and cook on Friday for Shabbos, we are simply continuing what was started Erev Yom Tov(2). The eruv serves as a reminder that only Shabbos preparations are permissible on Yom Tov(3).

2.If one did not make an eruv he may not cook on Yom Tov for Shabbos(4). For possible solutions to this dilemma, see D5, and E below.

3.The eruv only permits one to prepare on Yom Tov for Shabbos. On the first day of Yom Tov it is forbidden to cook or prepare for the second day(5).

4.When Yom Tov is Thursday and Friday, one may only start preparing for Shabbos on Friday(6) or even Thursday night(7), but not on Thursday.

5.When cooking for Shabbos, one should aim to allow enough time so that all the food would be edible on Friday, before the onset of Shabbos(8).

B.The contents of the eruv

1.The eruv consists of matza or any bread, and a cooked food, such as fish, meat or a hard-boiled egg(9). Usually, a hard-boiled egg is used.

2.The food being used for the eruv should preferably be cooked on Erev Yom Tov(10). Also, l'chatchila it should be cooked with the intention to be used for the eruv(11). This applies only to the cooked food, and not to the bread/matza(12).

3.One should not set aside a large food item for the eruv if he intends to eat some of it on Yom Tov. Rather, he should designate a portion that is solely for Shabbos(13).

C. Procedure for making the eruv

1.The eruv should be made on Erev Yom Tov during the day(14). In case of necessity it may be made on the previous night(15). In extreme situations it may be made a few days before Yom Tov(16), however a beracha is not recited(17).

2.The correct procedure for establishing an Eruv Tavshilin is as follows:

One should hold the designated foods (preferably in the right hand(18)) during the entire procedure, i.e., from the beginning of the beracha until the end of the declaration(19).

3.First, the beracha Al Mitzvas Eruv is recited(20).

4.Next the declaration Bahadein Eruva (as printed in Siddurim) is said. This must be said in a language one understands(21). The declaration states that through this eruv we are permitted to cook, bake, insulate, light candles, make all preparations, and do anything necessary on Yom Tov for Shabbos(22).

5.The eruv should be kept in a secure place until it can be eaten on Shabbos. It may be eaten at any Shabbos meal, however, the preferred option is to use the matza/bread for the second loaf of Lechem Mishneh for Friday night and Shabbos morning. It should then be eaten at Seudas Shlishis(23).

6.If the eruv was lost or eaten before the Shabbos preparations were completed, one may no longer rely on this eruv. However if a kezayis remains, it is still valid(24).

D.Who requires an eruv?

1.Anyone who intends to do Shabbos preparations on Yom Tov requires an Eruv Tavshillin. However, one eruv suffices for the whole household, i.e., when the master of the house (or any other household member) establishes the eruv, his wife and children who reside in the house are included(25). Women can also establish an eruv which will include the male household members. It is a hiddur mitzva for women who intend to cook, to listen when the beracha bringing about the eruv is recited(26).

2.It is unclear as to whether guests or one's married children who are visiting for Yom Tov are automatically included in the eruv(27). Therefore they should either make their own eruv without a beracha, or the master of the house should intentionally include them in the eruv following the procedure mentioned below in D4 for making an eruv on behalf of other people(28).

3.One who intends to only light candles for Shabbos but not to cook should make an eruv but without reciting a beracha(29).

4.One can establish an eruv on behalf of others either by including them in his eruv or by making one especially for them.

An eruv is only valid if the designated food items belong to whomever the eruv is intended. This can be accomplished in the following manner. An adult who is not an immediate member of the household(30) lifts the eruv foods one tefach(31), approximately 10cm(32), with the intention of acquiring a share in the eruv food for all those who are going to be included in the eruv.

Afterwards the one establishing the eruv follows the usual procedure. While holding the eruv he recites the beracha and then the declaration "Bahadein eruva...", and then adds the following; "lanu u'lechol Yisroel hadarin b'iyr hazos" - "for ourselves and for all Jews who reside within this city(33)". He can also choose to instead simply mention the individuals to be included in the eruv by name(34).

5.The Rav of the shul or city makes an eruv on behalf of all the town's inhabitants. He does this following the procedure for making an eruv on behalf of others (detailed in 4 above). If a town dweller forgot to make an eruv or their eruv was lost they can rely on the Rav's eruv(35).

6.However someone who was negligent is not included in this eruv(36). Someone who forgets to make an eruv once, may rely on the Rav's eruv but if he subsequently forgets, he is considered negligent and cannot rely on the community eruv(37).

Some explain this forgetting twice to mean that he forgot to make an eruv two Yomim Tovim in a row. If on the second Yom Tov he remembered to make an eruv and on a subsequent occasion he forgot, then he may use the Rov's eruv(38). One may rely on this opinion(39).

E. What to do if someone forgot to make an eruv

1. If someone forgot to make an eruv and he remembered after he left to go to shul but before Yom Tov, he should do one of the following:

a) Telephone home and ask another member of the household to make the eruv(40).

b) Go home to make the eruv himself as long as he will not thereby miss davening mincha with a minyan(41).

c) Go to a house nearby and make the eruv there (after receiving an egg and matza as a gift(42) ).

d) If none of the above are possible, one can establish the eruv in shul and say the following:
"Pas v'tavshil she'ekechnu k'she'eva livaisi, yihiye mei'achshav li'eiruv tavshillin" - "the bread and cooked food that I shall take when I return home should from this moment be considered an Eruv Tavshilin". With this option, a beracha may not be recited. Upon returning home, one should set aside the designated food for the eruv(43).

2.Bidi'eved, one can establish an eruv after sunset during twilight as long as the stars have not come out(44). He can also recite the beracha(45).

3.By davening Maariv with a minyan, one accepts Yom Tov and cannot thereafter make an eruv. However, if one accepts upon himself that it is Yom Tov only verbally and it is not yet night, he can still make the eruv(46).

4.After a woman has lit candles for Yom Tov and recited the beracha Shechechiyanu, she can no longer establish an eruv(47) though she can still tell others to make one for her(48).

5.If one only remembered once it is Yom Tov, and Yom Tov is Thursday and Friday then on Thursday one can make an eruv making the following stipulation: If Yom Tov is actually today, then tomorrow (Friday) is a weekday and an eruv is not needed to permit Shabbos preparations. On the other hand, if today is really a weekday and tomorrow is Yom Tov (in which case an eruv is indeed required) then this eruv shall be effective. Then one makes the eruv declaration Bahadein eruva etc. (49). This procedure is done without a beracha(50) and cannot be performed on Rosh Hashana or if the first day of Yom Tov is Friday(51).

SOURCES

1.Pesachim, 48b.
2.Rashi to Beitza 15b.
3.Beitza, 15b. This is R' Ashi's explanation. Rava gives a different reason. One might become too preoccupied with his Yom Tov preparations, and will disregard Shabbos. Chazal instituted an Eruv Tavshilin so that one won't forget to properly honour Shabbos. However the Mishna Berura (M.B.) 527:25 and also the Sha'ar Hatzion 527:35 say that the main reason follows R' Ashi's explanation. The Aruch HaShulchan 527:4 also says that the halacha follows R' Ashi's opinion.
4.Shulchan Aruch (Sh.A.) 527:20.
5.See Sh.A, 503. It states there that one may not prepare on the first day of Yom Tov for the next day. The second day of Yom Tov has the status of possibly being a weekday. If so he might be preparing on Yom Tov for a weekday.
6.Sh.A. 527:13.
7.Eruv Tavshilin HaAruch 21:1.
8.M.B. 527:3, Biur Halacha on 527:1.
9.Sh.A. 527:2. There is a hiddur mitzva to use a whole matza or bread.
10.See Biur Halacha, 527:14 S.V. L'chatchila, quoting the Beis Yosef.
11.See Biur Halacha, 527:6 S.V. Adashim, quoting the Bach.
12.Piskei Teshuvos 527:15. This is implied from the Poskim, because the main part of the eruv is the cooked food, the lack of bread would not invalidate the eruv as explained there, (2).
13.HaRav Shlomo Zalman Aurbach zt'l quoted in Shmiras Shabbos K'Hilchasa Chapter 46, note 100, also Sefer HaZicharon Mivakshei Torah in memory of HaRav S.Z. Auerbach, Vol 1. Chapter 3.
14.Sh.A. 527:14, M.B. 527:44.
15.Eruv Tavshilin HaAruch 14:2.
16.Sh.A., ibid.
17.Eruv Tavshilin HaAruch, ibid, with note 13.
18.Ibid, 9:3 based on Sh.A. 306:4 who writes that anything ones makes a beracha on, should be held in one's right hand during the beracha. One may also place both food items in a plate and hold the plate in his right hand.
19.Ibid, 9:1 based on Sh.A. 527:12 who writes one takes (the food items) and recites the beracha and says "with this it should be permissible etc.". See Piskei Teshuvos 527, note 37 who quotes an opinion that one must hold the eruv and it does not suffice to have it placed before him.
20.Sh.A. 527:12. The M.B. 527:64 writes that not reciting the beracha does not affect the validity of the eruv.
21.M.B. 527:40.
22.Sh.A. 527:12, The Poskim dispute whether not mentioning the melachos would invalidate the eruv or whether it is only a mitzvah l'chatchila, to mention them. See Rema, 527:20 and M.B. 527:63.
23.M.B. 527:48, in accordance with the maxim that since an object was used for one mitzva, let another mitzva be performed with it.
24.Sh.A. 527:15.
25.M.B. 527:56.
26.Aruch HaShulchan 527:22.
27.Piskei Teshuvos 527:17, Eruv Tavshilin HaAruch 4:8, based on Biur Halacha 527:20, S.V. Mi Shelo Ireiv.
28.Ibid.
29.See Sh.A. 527:19 who quotes a dispute as to whether or not one requires an eruv to permit him to light candles. See Minchas Yitzchak 7:36. This is also the ruling of the Chazon Ish, quoted in Eruv Tavshilin HaAruch 2:8, note 23.
30.Sh.A. 527:10 with M.B.
31.Sh.A. 527:11.
32.Shiurei Hamitzvos L'HaChazon Ish
33.Sh.A. 527:8: M.B. 527: 32
34.See Kaf HaChaim 527:14, also quoted in Eruv Tavshilin HaAruch 10:8 B'dein eruva yihei sharei l'ploni u'l'kol bnei beiso l'afuyei etc.
35. Sh.A. 527:7.
36. Sh.A. Ibid.
37.M.B. 527:22.
38.Kaf HaChaim 527:48, B'Tzel HaChachma 6:91
39.See Aruch HaShulchan 527:18, Nitei Gavriel Hilchos Eruv Tavshilin.
40.Based on Sh.A 527:7 which states that there is a mitzva on everyone.
41.M.B. 527:4.
42.Mateh Efraim 625:37.
43.Tiferes Yisrael, Beitza 2:1, Boaz 2, based on the principle that we say b'reira in Rabbinic issues. However, some are of the opinion that the eruv is only valid if one holds the foods whilst establishing the eruv. Still many Poskim agree with the Tiferes Yisrael. See Minchas Yitzchak 7:36, also HaRav S.Z. Auerbach zt"l quoted in Sefer HaZicharon Mivakshei Torah in memory of HaRav S.Z. Auerbach, Vol 1, Chap 4., and Laws of Yom Tov, Rabbi Simcha Bunim Cohen Chap 35, note 46.
44.Rema 527:1, M.B. 527:4.
45.See M.B. 261:11 with Biur Halacha.
46.M.B. 527:4.
47.Biur Halacha 527:1 S.V. Safek chasheicha is in doubt when a woman accepts Yom Tov through lighting candles. Does her kabbala have the status of a public kabbala (in which case she could not make an eruv) or the status of an individual (in which case she can make an eruv)? However, Sefer Halichos Beisa 17:4 writes that when one recites the beracha Shechechiyanu, one accepts upon themselves kedushas Yom Tov and one cannot make an eruv.
48.Piskei Teshuvos 527:4.
49.Sh. A. 527:22.
50.M.B. 527:74 says it is a dispute. Therefore we follow the rule, safek berachos l'hakel. When in doubt we do not make a beracha.
51.Sh. A. ibid.