Tzitzit or tzitzis (Hebrew: ציצית) are "fringes" or "tassels" worn by observant Jews on the corners of four-cornered garments, including the tallit (prayer shawl) and tallit katan. Since they are considered by Orthodox tradition to be a time-bound commandment, they are worn only by men
Source of Requirement
- There is a positive Torah commandment to place Tzitzit strands on a four cornered garment that one wears. 
- There is, however, no obligation to wear such a garment in the first place. Nevertheless, our Rabbis have strongly promoted the observance of this relatively simple Mitzvah since it comes with great reward.
- The obligation applies to all Jewish men age 13 and up.
- A blind man is equally obligated, and he should recite a bracha. It would be best for him to first feel and check the validity of his Tzitzit or ask someone else to confirm it for him.
- Women are exempt, as Tzitzit is a positive time bound mitzvah.
- A Katan, or minor child who is less than 13 years old, should wear tzitzit, with a bracha, once he reaches the age of chinuch .
- The earliest time to say a bracha on Tzitzit is from the time period that there is enough natural light so that one is able to distinguish between the white and blue strands within a clump of Tzitzit. This time period is also known as the time when one is able to recognize an acquaintance from 4 cubits away. Both descriptions are equivalent and commonly referred to as Misheyakir. There is a wide range of opinions precisely when Misheyakir occurs on a perfect day in Jerusalem: 35 minutes before sunrise, 60 minutes before sunrise, and 66 minutes before sunrise. The various opinions would then have to be extrapolated according to the region of the world and time of year. Thus, according to the commonly accepted opinion that Meshiyakir is between 50 and 60 minutes before sunrise in Jerusalem - In New York, depending on the time of the year, it could be anywhere from 56-73 minutes before sunrise.
- If one is pressed for an earlier time for work or travel reasons, there are opinions that one may make a bracha on Tzitzit already from dawn. Dawn is 72 equivalent minutes, or 1.2 seasonal hours, before sunrise. However, most modern poskim qualify that one shouldn’t rely on these minority opinions unless under “extreme circumstances” and should rather wait at least until the most lenient interpretation of Misheyakir.
- One may wear Tzitzit before these times, however he should do so without making a bracha, and only when it becomes the time period known as Misheyakir may one make a bracha.
- If one inadvertently made a bracha before dawn, he should not repeat another bracha when the correct time arrives.
- In terms of nighttime wear, one may wear Tzitzit at night without a bracha and can even sleep in them. He wouldn’t have to be worried about violating Baal Tosef. In fact, according to kabbalistic sources, Tzitzit protect a person at night from destructive forces
- However, one should not wear a Tallit Gadol at night, unless one is the shliach tzibur (cantor) for Maariv and he isn’t wearing an appropriate outer garment (like a jacket).
- Another exception would be for Sephardim, where it is customary for a chatan (groom) to wear a Tallit Gadol at his wedding ceremony, he may do so even at nighttime. If it is before sunset he should make a bracha and if after sunset then without a bracha.
- If you remove your tzitzit with intent to put them back on, you don’t make a new Bracha upon putting them back on if it’s within a half hour of when you took it off. 
- Sephardim generally follow the opinion of the Shulchan Aruch that only garments made of wool or linen have a torah obligation to be affixed with tzitzit strands. Accordingly, all other materials only require tzitzit on a rabbinic level. As such, it is preferable for one to wear a wool or linen garment. Nevertheless, it one finds it uncomfortable to wear wool tzitzit, he may wear tzitzit made from other materials.
- Ashkenazim rely on the Rema who holds that all materials are included in the Torah obligation. Nevertheless, some maintain that one still should wear wool and linen garments in order to satisfy all opinions. One the other hand, many poskim are lenient if wearing wool would cause any discomfort, especially in the heat.
- Although the Shulchan Aruch includes linen as a biblically mandated material, he also cites an opinion that we should not use it. He concludes that although the halacha is not like this opinion, it is preferable to avoid the argument and only use wool. However, if one only has a linen garment for his tzitzit, they may be used with a bracha.
- Leather garments are exempt from the obligation of tzitzit, even on a rabbinic level.
- Along the same lines, some poskim equate leather with synthetic materials (such as polyester, nylon, and rayon) and maintain that they are also exempt from tzitzit. Others differentiate between woven synthetic materials, which should be treated like cotton, and non woven synthetic materials, which should be treated like leather. Therefore, it is best not to use synthetic materials for the mitzvah, but if one does he should refrain from making a bracha on it.
- There are various opinions as to how big the garment needs to be to qualify as a halachically bona fide garment, so that one could make a bracha on them without worrying if it is a bracha levatala (in vein or wasted blessing): 1 amah by 1 amah, 1.5 amot by 1 amah , 1.5 amot by 1.5 amot, 2 amot by 1 amah, and finally there is even an opinion that there is no size requirement at all.
- Additionally, there are two different opinions for the conversion of one amah, or 6 tefachim (fists), to modern measurements: Rav Chaim Na’eh holds it is 48 cm or 18.9 inches, while the Chazon Ish holds it is 57.7 cm or 22.7 inches.
- Additionally, there is a dispute if the dimensions include or exclude the center hole for one’s head and neck. The Mishna Berura  doesn’t include the neck hole in the measurement, while the Chazon Ish  does.
- Halacha Le'Maaseh:
- Sephardim: To fulfill Mitzvah BUT not to make a bracha: should wear tzitzit measuring 1.5 amot by 1 amah. It would also be best if this shiur doesn’t include neck hole, but if it’s difficult to find a tzitzit that size or uncomfortable to wear, one may rely on the opinions that the neck hole is included. In this case, one should make a bracha on a tallit Gadol and patur (exempt) the tallit katan. In order to make a bracha on a tallit katan, it should measure 2 amot by 1 amah, which is 37.8 by 18.9 inches. .
- Ashkenazim: To follow the Mishna Brurah, preferably one should wear Tzitzit that 1 x 1 amah, however it should be at least 1.5 by 0.75 amah not including the neck hole.  Accordingly, one can wear a Tzitzit 32 by 16 inches not including the neck-hole.  Rabbi Willing is lenient to allow 26 inches in length. 
Sleeping in Tzitzit
- One who slept in his Tzitzit, shouldn’t make the Bracha on the Tzitzit but rather should make it on the Talit and that will cover the Tzitzit also.  However, if one doesn’t have a talit (as is the minhag of Ashkenazim prior to marriage), one should make the Bracha on the Tzitzit and it’s preferable to feel the tzitziyot when making the Bracha. 
- It’s proper according to kabbalistic sources, to wear one’s Tzitzit to sleep. 
- If one sleeps in one’s Tzitzit, it’s preferable to use those Tzitzit for the day as well sometimes, or for some time in the morning besides just using it for the night.  However, if one does have specific Tzitzit for the night only, one has what to rely on. 
- The minhag is to sleep in Tzitzit and not be concerned with disgracing the Tzitzit. 
- Bamidbar 15:38; Devarim 22:12
- Rambam Hilchot Tzizit 3:11; Tur 24:1; Shulchan Aruch 24:1
- Rambam Hilchot Tzizit 3:11; Tur 24:1; Shulchan Aruch 24:1; Rav Moshe Feinstein in Igres Moshe 4:4; Rav Ovadya Yoseh in Yechaveh Daat 4:2
- Mishna Berura 17:10
- Shulchan Aruch 17:1
- Mishna Berura 17:1
- Rabbi Shimon in Gemara Menachot 43a; Shulchan Aruch 17:2. The Rema (ad loc.) comments even though women are exempt, if they want, they may rely upon the opinion of Tosofot on Kiddushin 31a who would allow a woman to wear and make a bracha on Tzitzit. The Rema continues, however, that women still should not do so, since it would appear as arrogant and further that Tzitzit is not a personal obligation anyway. The Mishna Berura (17:5) elaborates that although women may rely on Tosofot for Lulav and Sukkah, Tzitzit are different since even men aren’t required from the Torah except if they wear a four cornered garment. We treat Tzitzit both as and as not a personal obligation towards leniency. Hence, it is a personal obligation in the sense that only if one wears the garment does he need to attach Tzitzit and not just when he owns a garment. And, it is not a personal obligation that one would need to go out and buy a four cornered garment just to perform the mitzvah. Therefore, since men don’t really have to, women certainly shouldn’t do so. Lastly, there is a possible concern of violating Beged Ish as Targum Yonatan Ben Uziel raises on Devarim 22:5. The Levush (17:2) and Ben Ish Chai (Lech Lecha 3) use similar logic.
- The Shulchan Aruch (17:3) doesn’t specify an exact age, rather the idea is once a child knows how to properly wear the tzitzit so that two strings are behind him and two in front (Rema 17:3)
- Shulchan Aruch 18:3
- Meaning that there is exactly 12 daylight hours and every seasonal hour consists of 60 minutes.
- Rav Moshe Feinstein in Le-Torah ve-Hora'ah Vol. 3:7
- Rav Tukaczinsky in Eretz Yisrael 1:4
- Rav Ovadya Yoseh in Yechaveh Daat 2:8
- There are two factors at work here: First, the processes of daybreak and nightfall occur faster at places near the equator than places further away from the equator. Second, the speed of these processes are also affected by the seasons. A common solution would be to use seasonal minutes. In order to calculate a seasonal hour, one would need to add up all the daytime minutes and then divide by 12 to get the number of minutes that are in each seasonal hour. For instance, if there were 11 hours of daylight, each seasonal hour would consist of 55 minutes. To further complicate matters, there are two ways of counting the daytime minutes: The Magen Avraham counts from dawn until nightfall with the emergence of 3 stars, whereas the Gra counts from sunrise to sunset. Another means for calculation, which has only recently been implemented, is to compare the level of brightness by using the relative position of the sun. For instance, it has been determined that 60 minutes before sunrise on a perfect day in Jerusalem the sun is 12.9 degrees below the horizon. Therefore, if one wanted to find the equivalent time anywhere in the world during any season, he would simply determine at what time the sun will be 12.9 degrees below the horizon in that locale on that day and that would be the extrapolated Meshiyakir.
- MyZmanim.com. These figures are determined using MyZmanim’s earliest published position of 11.5 degrees below the horizon. Unfortunately, MyZmanim.com only offers calculations based upon 10.2 degrees, 11 degrees, and 11.5 degrees but not 12.9 degrees. It is unfortunate because 12.9 degrees correlates to Rav Tukaczinsky’s 60 minutes before sunrise which, although is a very lenient position is also well collaborated and accepted.
- Mordechai on Gemara Megilla 2; Rema 18:3
- Rambam in Peirush HaMishnaiyot Berachot 1:1; Shulchan Aruch 459:2
- Gra 18:5; Mishna Berura 18:10
- Rav Ovadya Yosef in Halacha Berura 2, 30:1.
- Rema 18:3
- Mishna Berura 18:10. He explains that we are cautious since perhaps the halacha follows the Rosh that daytime garments worn at night require Tzitzit and accordingly the bracha would have been correct; Kaf HaChaim 18:22; Halacha Berura 1, 18:6
- Tosfot Gemara Niddah 51b; Rambam Hilchot Tzizit 3:8; Rema 21:3; Mishna Berura ad loc; Yalkut Yosef Additions 1, 8:5
- Rambam Hilchot Tzizit 3:8; Kesef Mishna ad loc; Beit Yosef 8:13
- Shaar Kavanot Tefilat Arvit:1
- Bach 18; Magen Avraham 18:1; Mishna Berura 18:4; Birkay Yosef 18:1
- Pri Megadim in Ashel Avraham 18:1; Mishna Berura 18:4
- Halacha Berura 1, 18:2
- Sh”t Otzrot Yosef 1:28
- 9:1. This is based off of Rav Nachman in Gemara Menachot 39b and is purported by the Rif and Rambam
- Rav Ben Zion Abba Shaul in Ohr LeZion 9:1; Rav Ovadya Yosef in Yalkut Yosef 9:1
- This is based off of Rava in Gemara Menachot 39b
- Mishna Berura 9:5
- Rav Moshe Feinstein in Igres Moshe 2:1; Similarly, The Vilna Gaon (Maaseh Rav Birchot HaShachar, 17) and the Chazon Ish (Shoneh Halachot 9:1) wore non-wool garments for their tzitzit
- 9:6; Also Kaf HaChaim 9:16. This opinion stems from Rabbenu Tam in Gemara Shabbat 25b
- Rema and Mishna Berura ad loc. This opinion comes from Teshuvot HaRosh 2:8
- Gemara Menachot 40b. Shulchan Aruch 10:4
- Rav Moshe Feinstein in Igres Moshe 2:1
- Rav Tzvi Pesach Frank in Har Tzvi 1, 9
- Tzitz Eliezer 12:3; Ohr LeZion 2:3
- This range emanates from the Gemara Menachot 40b dictate that the garment needs to be the size that it would cover the head and majority of a minor. First off, there are different interpretations as to how old this minor is: The Chinuch (Shelach: 386) and Bach (16) say the reference is to a 6 or 7 year old, the Tur (16) says 9 years old, and the Radbaz (6, 2:106) explains it to be a 5 year old. Second of all, there is ambiguity if the majority requirement means that the garment needs to cover the head and then in addition a majority of the kid’s body (Radbaz) or if it only needs to cover in total a majority of the kid with the head included (Chinuch). Meaning, it would be sufficient to cover the kid’s head and another 30 or 40% of his body, as opposed to 51%
- Pri HaAretz 1; Beit David 8; Shalmei Tzibur 26b; Pri Ha’Adoma 23a; Nachal Eshkol pg. 102:4 ; Ha’Elef Lecha Shelomo 1:4.
- Chazon Ish 3:31; Rav Pe’alim 2:6; Mishna berura 16:4;
- Lev Chaim 1:99;
- Siddur of Rabbi Shneur Zalman, the author of Shulchan Aruch HaRav and The Tanya. Similarly, the Gra, without specific numbers, was very strict in this regard and required the garment extend down to one’s knees. Also, the Chazon Ish (ibid) concludes that it is best to follow this size requirement. Likewise, the Mishna Berura (8:17, 16:4) suggests this size to avoid difference of opinions.
- Aruch HaShulchan 16:5
- 8:17, 16:4
- See Halacha Berurah 1, 16:1; and “Tzel Heharim” by R’ Hertzel Hillel Yitzhak, p. 8-11, (http://books.google.com/books?id=smV4tK-2BmAC&pg=RA1-PA8&lpg=RA1-PA8&dq=size+of+tallit+katan+amah&source=bl&ots=WIS4hgNl6j&sig=kueGC117C5r8YA8ytsF8FatCRaU&hl=en&ei=odrBS5GSBs2blQeS5pWaCQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CA0Q6AEwAA#v=onepage&q=size%20of%20tallit%20katan%20amah&f=false) who measures the standard of an Amah according to Rav Chaim Noeh.
- Mishna Brurah 8:17, 16:4
- Rabbi Neusadt, author of Daily Halacha Discussions, writes that using Rav Moshe's (Sh"t Igrot Moshe 1:136) standard of measuring the Amah which is 21.3 inches per Amah one ends up with 32 inches by 16 inches. http://www.torah.org/advanced/weekly-halacha/5765/pekudei.html
- http://www.yutorah.org/lectures/lecture.cfm/729840/Rabbi_Zvi_Sobolofsky/Hilchas_Tzitzis_Part_2_(definition_of_a_cornder,_size_of_beget,_straps,_brecha_on_borrowed_tzitzis) at 14 minutes, Rabbi Sobolofsky in name of Rabbi Willig
- S”A 8:16 writes that one who slept in his Tzitzit may make a Bracha on it in the morning. Mishna Brurah 8:42 writes that since some argue on this it’s better not to make the Bracha on the Tzitzit but rather to have it in mind when one makes the Bracha on the talit.
- S”A 8:16 writes that one may make a Bracha on Tzitzit that one slept in and it’s proper to feel the tzitziyot when making the Bracha. Piskei Teshuvot 8:30 writes that if one doesn’t have a talit one may make the Bracha on the Tzitzit.
- Mishna Brurah 21:15 writes that the Arizal holds that it’s important to sleep in one’s Tzitzit according to the kabbalah. So writes Magan Avraham 21:2, and Kaf HaChaim 21:15
- Piskei Teshuvot 21:5 writes that one should be careful to sleep in Tzitzit that are also used for the day because otherwise one wouldn’t fulfill the mitzvah according to any opinion (since the Rosh holds that there’s a mitzvah of Tzitzit at night using clothing of the day and Rambam holds that there’s only a mitzvah during the day). So writes the Torat Chaim Sofer 21:5, Sh”t Vayivarech David 1:5, Kaf HaChaim 21:15. (Piskei Teshuvot also quotes the Hagot Rabbi Akiva Eiger (M”A 2) and Eshel Avraham who agree).
- Sh”t Shevet Halevi 6:50, 10:2 writes that it’s only a chumra not to use Tzitzit designated for the night. So writes Hagot Baruch Taam on S”A, Sh”t Kinyan Torah 4:1, Siach Halacha (Siman 21) in name of Rav Shlomo Zalman, and Piskei Teshuvot 21:5. Sh”t teshuvot VeHanhagot 2:9 writes that it’s preferable if there’s some light in the room because there’s an opinion that if there’s light in the room, at night one’s obligated in Tzitzit. Another advise given by Sh”t Teshuvot VeHanagot 1:19 (brought in Piskei Teshuvot 21:5) is that one should have intent that one fulfill the mitzvah of Tzitzit while one’s sleeping once dawn comes.
- Rama 21:3, Yalkut Yosef (Sherit Yosef 8 note 4).