The Nine Days is time period from the beginning of the month of Av until Tisha BeAv during which there are a number of practices of mourning described below. While many of the laws below apply to the entire period of the Nine Days, some of them only apply during the week in which Tishba BaAv falls out (Shevua SheChal Bo). Additionally, these practices are very similar but generally more stringent than those that observed during the Three Weeks.
- From the beginning of the month of Av one should reduce one’s involvement in activities of happiness. 
- If one has a lawsuit with a non-Jew one should delay it until the month of Elul or at least until after Tisha BeAv.  Similarly, if one must have a surgery and it can be delayed, one should try to delay it until after Tisha BeAv.
- During the Nine Days, one should refrain from buying materials that are needed for a wedding. Some authorities are lenient if the groom has not yet fulfilled the mitzvah of Pru Urevu and one will not be able to prepare for the wedding after Tisha BeAv because the wedding is right after Tisha BeAv or if there is a concern that the price of the wedding needs will become expensive after Tisha BeAv.
- The minhag is to be lenient to allow one not to reduce one’s regular business during the Nine days. 
- One may not build houses or buildings for business purposes during the Nine Days. However, one may hire a non-Jew before the Nine Days with a fixed sum for the entire project and then, he may work during the Nine Days and even on Tisha BeAv. 
- If a wall is going to fall, even if there isn’t a concern of danger but only a concern of loss, one may restore it during the Nine Days. 
- If there is a need, one may buy furniture if it is going to be delivered after the nine days.
- One shouldn't buy important items such as furniture or appliances during the nine days since it brings a person a lot of pleasure.
Taking Haircuts and Shaving
- The Sephardic minhag is not to take a haircut during the week in which Tishba BaAv falls out (Shevua SheChal Bo), while the Ashkenazic minhag is not to take a haircut during the entire Nine Days. 
- Shaving one’s beard or mustache is forbidden just like it is forbidden to take a haircut.  If one moustache interferes with one’s eating, one may cut it. 
- It is permitted to comb and style one's hair during the Three Weeks and Nine Days and one doesn't have to worry that one will pull out hairs. 
- If Tisha BeAv falls out on Shabbat and is pushed off until Sunday, according to Sephardim, it's proper not to take a hair cut the week prior to Shabbat Chazon. However, in regards to shaving, if one shaves regularly and it's difficult not to shave, one may shave during the week before Shabbat Chazon, especially if one is doing so for Kavod Shabbat. 
- The Sephardic minhag is not to launder clothes or wear newly laundered clothes during the week in which Tishba BaAv falls out (Shevua SheChal Bo), while the Ashkenazic minhag is not to launder clothes or wear newly laundered clothes during the entire Nine Days. 
- Some say that one may prepare one's clothing for the week in which Tisha BeAv falls (Shevua SheChal Bo) by changing one's clothing on Shabbat Chazon so that one has enough clothes to wear during the next week.
- If Tisha BeAv falls out on Shabbat and is pushed off until Sunday, according to most Sephardim, one may launder clothing and wear laundered clothing the week prior to Shabbat Chazon. However, Ashkenazim don't wear laundered clothing the entire Nine Days in any event. 
- If one was not able to change clothes on the day before the prohibition against wearing clean clothes began, another option is to drop clothing on the floor before putting it on.
Showering, Bathing, and Swimming
- The minhag in some places is to refrain from bathing during the week which Tisha BeAv falls out and some places have the minhag not to bathe during the Nine Days. The Sephardi minhag is only to refrain from bathing in warm water during the week which Tisha BeAv falls out, while the Ashkenazic minhag is to avoid pleasure bathing all 9 days.
- The Ashkenazic minhag is not to go swimming in the Nine Days.  The Sephardic minhag, however, is to refrain from swimming in cold water during the week in which Tisha BeAv falls (Shevua SheChal Bo). 
Eating Meat and Drinking Wine
- The Ashkenazic and Sephardic custom is to refrain from meat, poultry, and wine during the nine days. Ashkenazim include Rosh Chodesh in this prohibition, while Sephardim are lenient regarding the day of Rosh Chodesh itself and some Sephardim are strict. 
- Some say that there is what to rely on to have meat leftovers from Shabbat during the nine days, while others forbid. 
- One who needs to eat meat for health reasons such as a child, pregnant woman, nursing woman, or an elderly or sick person is permitted to eat meat, but if he can eat chicken that is preferable. 
- One may eat meat at a meal for a mitzvah such as the meal of a Brit Milah and this includes the relatives and friend invited to the meal however, it doesn’t include those who just walk in to eat. 
- One may eat meat at a meal held for a siyum and this includes the friends and family invited to the meal. 
- One may eat meat a meal held for a Bar Mitzvah only if it’s held the day that the son becomes 13. 
- It is preferable not to even feed children meat during the nine days, but if you do you may have on who to rely. 
- Although the custom is not to eat meat or drink wine during the nine days, stores that sell meat or wine may continue to sell meat or wine because someone who is permitted to eat it, such as a sick person or for a seudat mitzvah may need it.  One is permitted to leave his meat restaurant open during the nine days, because the people who are eating meat during the nine days, without the availability of kosher meat, may go to a non-kosher restaurant but he should preferably serve only chicken. 
- One may taste the meat food on erev shabbat during the nine days but should try not to swallow any meat ingredients. 
- One is permitted to buy meat and wine during the Nine days for use after the Nine days if there is a sale, or he won't have time afterwards. 
- One is permitted to eat food that was cooked in meat pots, as long as not meat was cooked with it, and one cannot taste the taste of the meat in his food.  Parve food which looks like meat may be eaten during the Nine Days. 
- If, by mistake, one recited a blessing over meat or wine, he should taste a bit so that his blessing will not have been in vain. 
- Since the minhag is not to drink wine, a question arises as to what we should do with Havdalah. For sephardim one is permitted to use wine and drink it as usual  while for Ashkenazim there are several possibilities. 
- Even somebody who normally uses a cup of wine for Birkat HaMazon, should not during the nine days except for on Shabbat. 
- One may eat meat on Shabbat during the Nine Days.If one began a meal on Shabbat and it continued into the night, one may continue to have meat, however, some are strict in this situation.
Trips and Pleasurable activities
- S”A 551:1
- S”A 551:1, Mishna Brurah 551:2
- Yalkut Yosef (Moadim p. 557)
- Mishna Brurah 551:11
- Yalkut Yosef (Moadim p. 558)
- Mishna Brurah 551:11, Yalkut Yosef (Moadim p. 559)
- S”A 551:2, Mishna Brurah 511:12
- S”A 551:2, Mishna Brurah 551:13
- Halichot Shlomo (p. 426, 14:22)
- Guidelines of the Three Weeks by Rabbi Elozor Barclay (p. 47) citing Igrot Moshe 3:80 and MeBeyt Levi p. 8 n. 4
- S”A 551:3, Yalkut Yosef (Shevua SheChal Bo #1)
- Rama 551:3
- S”A 551:12
- S”A 551:13
- Eliya Rabba 551:7, Shaare Teshuva 551:12, Mishna Brurah 551:20, Aruch Hashulchan 551:15, Sh"t Yachava Daat 6:35
- Yalkut Yosef (Shevua SheChal Bo #11), Yechave Daat 3:39
- S”A 551:3
- Rama 551:3
- Orchot Rabbenu (vol 2, p. 130) quoting the Stiepler
- Yalkut Yosef (Shevua SheChal Bo #11), Yechave Daat 3:39
- S”A 551:16
- Yalkut Yosef 551:13
- Rama 551:16
- Sh"t Teshuvot VeHanhagot 2:263, Piskei Teshuvot 551:46
- Some Poskim agree that it is OK to go swimming for exercise, but not for fun.
- Yalkut Yosef (Shevua SheChal Bo #14) writes that strictly speaking the Sephardic minhag would allow swimming in cold water during Shevua SheChal Bo, however, because of danger it's proper to refrain from it. This is the position of Rav Ovadya Yosef in Sh"t Yachava Daat 1:38. Rabbi Mansour on dailyhalacha.com however, writes that swimming during Shevua SheChal Bo is forbidden because of bathing. See also Or Letzion.
- The gemara Baba Batra 60b quotes the opinion of Rabbi Yishmael Ben Elisha that after the destruction of the Beit HaMikdash, it would have been appropriate for the rabbis to ban eating meat and drinking wine in order to properly mourn. However, since most of the congregation would not be able to abide by this, the rabbis never made it. Biur HaGra OC 551:9 writes that this is the source for refraining from eating meat and drinking wine prior to Tisha B'Av, that although it is impossible to ban eating meat and drinking wine throuvghout the year, it is possible to refrain from meat and wine for a short period of time. The Mishna in Taanit 26b the Gemara 30a discuss the prohibition of eating meat during the seudat hamakseket prior to tisha b'av. Rambam Hilchot Taaniot 5:6 says that the custom is to extend the prohibition beyond that meal. He says that some don't eat meat during the week of tisha b'av, and some don't eat from rosh chodesh av and onward. Shulchan Aruch 551:9 writes that there are three customs about not eating meat and drinking wine; some refrain only for the week on Tisha BeAv, some refrain for the nine days (from Rosh Chodesh Av), some refrain for the whole three weeks. Mishna Brurah 551:58 writes that the Ashkenazic custom is not to eat meat or drink wine for the nine days including Rosh Chodesh Av but excluding Shabbat (Mishna Brurah 551:59). This is also written in the Weekly Halacha by Rabbi Neustadt. Sh"t Yachava Daat 1:41, Moed Likol Chai 9:15, Rav Bentzion Mussafi, and Kaf Hachayim 551:125 write that the Sephardic custom is to refrain from eating meat and wine during the nine days, however, on Rosh Chodesh the minhag is to be lenient, however, some are strict. See also Chazon Ovadyah (Arba Taniyot pg 169), Rabbi Mansour on dailyhalacha.com, and Halachot and History of The Three Weeks (by Rabbi Shlomo Churba, pg 37) who all write that the Sephardic custom is not to eat meat, poultry or wine in the nine days.
- Chazon Ovadyah (Arba Taniyot pg 177) writes that there is what to rely on, as does the Torat Moadim 5:46. Birkei Yosef 551:6 says that in order to encourage proper for fulfillment of the meal itself we allow the leftovers to be eaten later. However, the Weekly Halacha by Rabbi Neustadt quotes Sh"t Igrot Moshe 4:21(4) who forbids (see there). Aruch Hashulchan 551:24 also forbids it, also see Piskei Teshuvot 551:34. Kaf Hachayim 551:144 says that for melave malka one is permitted to eat meat leftovers as long as he doesn't prepare extra for shabbat with the intention of having leftovers. Rabbi Eli Mansour quotes that Rav Chaim Palachi allows this while Chacham Benzion Abba Shaul says it's better not to. Rabbi Mansour also says that for the remainder of the week kids can eat it lechatchila and if adults eat it one cannot rebuke them. Piskei Teshuvot 551:34 says there are some poskim who permit eating meat for melave malka for someone who usually eats meat for melave malka.
- Mishna Brurah 551:64. Yechave Daat 1:41 adds that if they do, they are not required to make a hatarat nedarim.
- Chazon Ovadyah (Arba Taniyot pg 196-7). Rama 551:10 allows eating meat for a seudat mitzva, and the Taz there explains that only someone would normally be invited to this seuda, may partake in this meat seuda during this time. If the bris is scheduled to be performed before the nine days, even if it has already been postponed, Shaare Teshuva 551:10 says you cannpot postpone any further to allow eating meat, and one who does this is considered someone who breaches fences.
- Chazon Ovadyah (Arba Taaniyot pg 196-8). Although the Rama 551:10 writes that one should minimize the amount of guests invited to this meal, Rav Moshe Feinstein and Rav Shlomo Zalman Auerbach (cited in Nitei Gavriel 18:7), rule that if the one who completes the masechet eats in a communal dining room (such as a camp or hotel), all those who eat with him may participate. Rav Moshe Feinstein quoted in Moadei Yeshurun page 132 says that preferably one shouldn't hold a siyum of a masechet after the sixth of av. Aruch Hashulchan 551:28 says that since nowadats we do not properly celebrate the torah, preferably no siyums should be held during the nine days.
- Chazon Ovadyah (Arba Taniyot pg 200), Halichot Shlomo (Moadim vol 2 pg 415), Yad Yitzchak 3:230, Yad Efrayim 551:31, Divrei Yatziv 2:238. Even though this is not mentioned by the Rama 551:10 as one of the meals you can eat meat for, Magen Avraham 225:4 says that a bar mitzva meal is a seudat mitzva, because just like siyum on a masechet is the celebration of the culmination of a mitzva, so too a bar mitzva is celebrating culminating the mitzva of chinuch.
- Magen Avraham 551:31 says you can give children meat even during the week of tisha b'av because we never had the minhag for kids to mourn. However, he adds that this is only true for a child below the age of chinuch, meaning a child who doesn't understand what we mourn. Mishna Brurah 551:70 and Shaar Hatziyun 551:76 say that although there is no requirement for the child to mourn for the beit hamikdash, the prohibition of feeding children prohibited items discussed in SA OC 343 extends to things that are only prohibited by custom and therefore one shouldn't feed meat to his kids unless for health reasons and the reason the Rama permitted Havdalah wine for children was for a mitzva. Iggerot Moshe 4:21:4 says even to feed the children meat on Friday afternoon before shabbat would not be allowed unless they usually eat their Friday night meal at that hour. Based on the Magen Avraham 551:31, Rabbi David Yosef in torat hamoadim Siman 5 page 190 says there is ample room to be lenient in this case. Aruch Hashulchan 551:26 as well says there is room to be lenient, especially in a case where it is a weak child who can gain a lot from eating the meat.
- Iggerot Moshe 4:112
- Yechave Daat 3:38. For more on whether a meat restaurant may remain open, see Rabbi Chaim Jachter: Restaurants Serving Meat During the Nine Days
- Shemirat Shabbat Kihilchita 42:61 since the Magen Avraham 250:1 quotes the Arizal that this is part of the mitzva of kavod shabbat to taste the food to make sure it tastes good.
- Iggerot Moshe 4:112
- Mishna Brurah 551:63, Kaf Hachayim 551:142, Orchot Chaim 31, Nitei Gavriel 38:5. Shaar Hatziyun 551:68 writes that even if a small piece of meat that will not be tasted fell into a dish, it may still be eaten.
- Nitei Gavriel 38:6
- Sdei Chemed (Bein ha-Metzarim 1:4). See also the topic of mistakenly making a Bracha on food on a fast day at Fast_Days#Other_Halachas_of_fast_days.
- Shulchan Aruch 551:10. Yalkut Yosef page 574 adds that one may drink the entire cup.
- The Aruch HaShulchan 551:26 says some people have the Minhag to drink beer or another drink that qualifies as Chamar Medina. The Eshel Avraham 551 and the Chazon Ish (quoted in Imrei Yosher, pg. 4) says that those who say Havdalah every week over wine or grape juice should do the same during the Nine Days as well. Rav Moshe Harari in his Mikraei Kodesh 1:14 say it is preferable to use grape juice as this doesn't cause any joy, and Rav Moshe Karp in Hilchot UMinhagei Ben HaMetsarim chapter 4 note 74 says that in this situation an adult can drink it lechatchila. Rama 551:10 says to preferably give it to a child. Mishna Brurah 551:70 says that it should be a minor above the age of chinuch but doesn't fully comprehend the concept of mourning the destruction of the beit hamikdash. Rav Moshe Feinstein quoted in Moadei Yeshurun page 154 says the adults should drink the Havdalah wine. Darkei Moshe 551:9 says in the name of the Maharil that this can be done lechatchila. See piskei teshuvot 551:35 and Hilchot UMinhagei Ben HaMetsarim chapter 4 note 74 for more poskim who say this.
- Rama 551:10 with Mishna Brurah 551:69, Kaf Hachayim 551:152.
- Shulchan Aruch 552:10
- Nitei Gavriel 38:4
- S”A 551:2
- Rama 551:2
- Yalkut Yosef (Moadim p. 560)
- Rivevot Efraim 1:374 quotes one gadol who said that it was forbidden to take pleasurable trips during the nine days. Afterwards, he writes that this is hard to understand and isn't included in the prohibition of binyan shel simcha.
- Rivevot Efraim 1:374 quoting Rav Moshe Bick, Rav Chaim Pinchas Scheinberg, and Rav Munk writes that it is permitted to cut one's grass during the nine days, but on Tisha BeAv itself one should be strict not to.
- S”A and Rama 551:7