This is the approved revision of this page, as well as being the most recent.
Source of Requirement
- For the source for tzitzit, see the Tzitzit page.
- The pesukim in Shalach  introduce the mitzvah of Tzitzit and among them is one that mentions the requirement to have a string of the Techelet color.
"דבר אל בני ישראל ואמרת אלהם ועשו להם ציצת על כנפי בגדיהם לדרתם ונתנו על ציצת הכנף פתיל תכלת"
Debate of Requirement Nowadays
- The Mishna (menachot 38a) writes that wearing Tzitzit without Techelet also fulfills the mitzvah of Tzitzit (while lacking a part of the mitzvah). This is codified in the Rambam (Tzitzit 1:3).
- From the end of the era of the sages of the Gemara Techelet became unavailable and extinct from common practice. However, in the last century and a half many have investigated this lost dye and some claim to have rediscovered it. The halachic question is how to deal with the dyes which some have claimed to be the real Techelet of the Torah.
- Rav Hershel Schachter in Ginat Egoz (Siman 2) writes that there is very little reason not to wear Techelet Tzitzit because of a doubt that perhaps it is the correct Techelet. He addresses the fact that the minhag is to wear a white garment with white strings, but says clearly that there’s no reason that this minhag should override a possibility to fulfill a biblical mitzvah. Furthermore, the Bet HaLevi (Sh”t Bet HaLevi 42) who says that there’s a prohibition of detracting from the מצות by fulfilling a mitzvah in a inferior way but that since a positive mitzvah overrides a negative one, there’s still reason to wear Tzitzit without Techelet because one still fulfills a positive mitzvah. Extending this further, Rav Schachter writes that if a person owns Techelet then it becomes possible to fulfill the positive mitzvah and negative one simultaneously and therefore one wouldn’t be allowed to use a positive mitzvah to override a negative one.
- There are other Poskim who hold of wearing Techelet but most don't hold it is as much as a Chiyuv as Rav Schachter. Rav Meir Mazuz, Rosh Yeshiva of Kiseh Rachamim in Bnei Brak, wears Techeles on Shabbos and Yom Tov as he holds it's not a Chiyuv rather a nice Chumra. 
- However, the overwhelming minhag for the last century was not to wear the Techelet which were suggested as the real species of Techelet. There’s a short article of Rav Elyashiv (Kovetz Teshuvot 1:2) who mentions several reasons to defend this practice. See Teshuvot vihanhagot 1:29 and 4:5 who quotes Rav Chaim Pinchas Scheinberg saying that future generations may think that we have had the tradition the entire time. Also, http://www.dailyhalacha.com/displayRead.asp?readID=785&txtSearch=techelet quotes Chacham Ben-tzion Abba Shaul who says that if your father and grandfather didn't wear a string of techelet than you should follow that practice as well. Rav Shlomo Aviner http://www.ravaviner.com/2011/06/techelet.html and in Shu"t She'elat Shlomo 4:12-20 also gives several reasons not to wear techelet. So does Rav Osher Weiss
- Firstly, the discoveries made regarding the Techelet have been inconclusive and the first two claims were later disproved and who’s to say that the new one which is claimed to be authentic will stand the test of time. Additionally, perhaps by the mere fact that for over a thousand years Jews haven’t used such a species for Techelet is a tradition that this species isn’t the correct one. Some sources even point to the fact that the secret of the Techelet was hidden after the destruction of the Bet Hamikdash. Lastly, how are we to determine the correct method in developing the dye if it’s disputed even in the early authorities and the dispute is left unresolved.
Number of Techelet Strings
The Radziner in Petil Techelet summarizes the dispute:
- Rambam holds that one string out of eighth are techelet. Sefer Hachinuch, Maggid Meisharim, Mabit, Maharam Ibn Gabay, Sefer Charedim, Levush, Gra, Sefer Hakaneh, and Arizal agree with the Rambam. Radziner in Petil Techelet ch. 6 ends up following the Rambam but says one has what to rely upon to follow either of the other opinions. Ben Ish Chai (Noach n. 17) and in Od Yosef Chay (Vaera n. 3) holds like the Rambam. Rav Meir Mazuz and Rav Yonatan Mazuz agree.
- Raavad holds that one string out of four (two out of eight) is techelet. Aruch (Techelet) agrees with the Raavad. Smag has safek like Tosfot or Raavad. Some achronim hold like the Raavad.
- Rashi and Tosfot hold that four strings out of eighth are techelet. Rav Schachter ("Hilchos Tzitzis" beginning) holds like Rashi and Tosfot and recommends all Ashkenazim to follow this method due to the plethora of sources advocating it (Baal haIttur, Tur, Shulchan Aruch, etc.).
There are several methods of tying tzitzit with techelet.
- Rav Amram Gaon: Rav Amram Gaon says that there shall be at least 7 links that each have 3 winds. After tying a knot closest to the garment, the first link should be white. Every link after should alternate in color. One can extend the pattern to 13 links if desired. Diagrams
- Raavad / Rav Natronai Gaon: The Raavad quotes Rav Natronai Gaon and holds that there should be 4 links and that each link has 7 winds. Each link is separated by a knot. The winds of each link should alternate white and techelet, the first and last wind of each link being white. The Raavad dictates that the link closest to the edge of the garment and the two links farthest from the garment must follow the alternating pattern. However, the unmentioned link can either be all white or the alternating white and techelet pattern. Diagrams
- Tosafot: Baalei Tosafot holds that one should use 7 links of 3 winds each, with 5 total knots separating them. Between the first and second knot, second and third knot, and third and fourth knot, there should be one link of white followed by one link of techelet. Between the fourth and fifth knot, one link of white should be used. Diagrams
- Rambam: The Rambam maintains that there should be between 7-13 links (chulyot) and that each link should have 3 winds (krichot). In the closest link to the garment, the first wind should be white, while the other two winds of that link should be techelet. In the farthest link from the garment, the final wind should be white, while the other two winds of that link should be techelet. All other links contain only techelet. Diagrams
- Sefer Hachinuch: The Sefer Hachinuch writes that there should be 13 links broken up by 5 double knots. The first 3 sections have 3 links, while the fourth has 4 links. Each section is broken up by a double knot. Diagrams
- Rav Hershel Schachter: There is an argument among Rishonim what the gemara means when it says we need between "7 and 13" for the tzitzit. Some say it refers to the number of links (chulyot) and others say number of winds (krichot). Rav Schachter incorporates each understanding by having 7 links of 7 winds each. Each link is separated by a double knot. the first three winds of the first link are white, and the last three winds of the last link are white (to satisfy Tosafot). All other winds are techelet (to satisfy Rambam). How to tie. Diagram
If the Strings Ripped
- If all white tzitzit, click here.
- According to the Rambam, if all white strings tore off up to the corner of the garment, and all that was left were techelet strings, the garment is still fit for use. 
- Bamidbar 15:38
- Rashi on this mishna interprets this differently. When the mishna describes that the lack of white doesn't invalidate blue or vice versa, Rashi says this means that the number of techelet and white strings must be equal.
- Kisei Rachamim's website
- Rambam Halachot Tzitzit 1:6
- Conflicts with most online resources. They say number of strings for Sefer Hachinuch should be 2/8.
- Ptil Tekhelet 6:15-16 based on the Gra's commentary to Zohar Pinchas 228, Sifra Ditzineuta Trumah 179b end of ch. 5, Raya Mehemna Shlach 175, and Biur Hagra O.C. 12:5.
- Raavad on Rambam Halachot Tzitzit 1:6
- Birurei Halacha Bmitzvat Techelet Shebetzitzit p. 63 n. 106 learns from the Rambam Tzitzit 1:5 that even if one uses more strings of techelet than are necessary one fulfills the mitzvah. p. 72 n. 117 he concludes to follow the Raavad since it is the opinion of many rishonim and the Rambam would agree.
- Rashi on Mishna of Menachot 38a. Rosh Hilchot Tzitzit n. 6 seems to agree.
- Goanika, v. 2 p. 331
- Raavad on Rambam Halachot Tzitzit 1:7
- Tosafot on Menachot 39a
- Rav Yonatan Mazuz writes that one should tie the techelet like one ties the white strings, with sections of 7, 8, 11, and 13 windings and knots in between. The only difference is that the first and last winding should be white and everything else techelet.
- Rambam, Halachot Tzitzit Chapter 1
- Sefer Hachinuch Mitzvah 386
- Note, the diagram interprets Chinuch as holding that each link should be three winds, which is not clear. Also, it interprets that the links should alternate colors, beginning and ending with white, which is also unclear from the Chinuch.
- YUTorah.org, Rav Hershel Schachter, "Details regarding the tying of Tekhelet"
- Rambam, Hilchot Tzitzit 1:4. He explains that this is due to the mishna on Menachot 38a saying that the absence of white does not invalidate blue and the absence of blue does not invalidate white.