Nusach Sefard, Nusach Sepharad, or Nusach Sfard is the name for various forms of the Jewish siddurim, designed to reconcile Ashkenazi customs (Hebrew: ? "Custom", pl. minhagim) with the kabbalistic customs of Isaac Luria.  To this end it has incorporated the wording of Nusach Edot haMizrach, the prayer book of Sephardi Jews, into certain prayers. Nusach Sefard is used nearly universally by Hasidim, as well as by some other Ashkenazi Jews but has not gained significant acceptance by Sephardi Jews. Some Hasidic dynasties uses its own version of the Nusach Sefard siddur, sometimes with notable divergence between different versions.
Some versions are nearly identical to Nusach Ashkenaz, while others come far closer to Nusach Edot Mizrach: most versions fall somewhere in between. All versions incorporate the customs of Isaac Luria.
There are many differences between the [various] prayer books, between the Sefardi rite, the Catalonian rite, the Ashkenazi rite, and the like. Concerning this matter, my master [the Ari] of blessed memory told me that there are twelve windows in heaven corresponding to the twelve tribes, and that the prayer of each tribe ascends through its own special gate. This is the secret of the twelve gates mentioned at the end of [the book of] Yechezkel. There is no question that were the prayers of all the tribes the same, there would be no need for twelve windows and gates, each gate having a path of its own. Rather, without a doubt it necessarily follows that because their prayers are different, each and every tribe requires its own gate. For in accordance with the source and root of the souls of that tribe, so must be its prayer rite. It is therefore fitting that each and every individual should maintain the customary liturgical rite of his forefathers. For you do not know who is from this tribe and who from that tribe. And since his forefathers practiced a certain custom, perhaps he is from that tribe for whom this custom is appropriate, and if he comes now and changes it, his prayer may not ascend [to heaven], when it is not offered in accordance with that rite.-- Sha'ar ha-Kavanot, Inyan Nusach ha-Tefila
It is generally held that every Jew is bound to observe the mitzvot (commandments of Judaism) by following the customs appropriate to his or her family origin: see Minhag. For this reason a number of rabbis disapprove of the adoption of Nusach Sefard by Ashkenazi Jews.
However, it was a common Kabbalistic belief that the Sephardic rite, especially in the form used by Isaac Luria, had more spiritual potency than the Ashkenazi. Many Eastern Jewish communities, such as the Persian Jews and the Shami Yemenites, accordingly adopted the Sephardic rite with Lurianic additions in preference to their previous traditional rites. In the same way, in the seventeenth and eighteenth centuries many Kabbalistic groups in Europe adopted the Lurianic-Sephardic rite in preference to the Ashkenazi. This was however the custom of very restricted circles, and did not come into widespread public use until the rise of middle to late 18th-century Hasidism.
Luria taught that twelve gates of prayer exists, corresponding to the twelve tribes of ancient Israel (and to the twelve Jewish communities that existed in Safed in Luria's lifetime), and that twelve nusachs for Jewish prayer (nasachot ha-tefillah) emanated accordingly. These
In alteration of this Lurianic concept, especially in 18th/19th-century Hasidic Judaism the claim emerged that, while in general one should keep to one's minhag of origin, the Nusach Sefard reached a believed "thirteenth gate" (Shaar ha-Kollel) in Heaven for those who do not know their own tribe.Nusach Sefard, with its variant Nusach Ari, became almost universal among Hasidic Jews, as well as some other Ashkenazi Jews, but has not gained significant acceptance by Sephardi Jews. One consequence of this was that, before the foundation of the State of Israel and in the early years of the State, it was the predominant rite used by Ashkenazim in the Holy Land, with the exception of certain pockets of traditional Lithuanian Jews. One reason for this was that Eretz Yisrael was regarded as part of the Sephardic world, so that it was felt that new immigrants should adapt to the local rite. In recent decades, following the immigration of many Ashkenazi Jews from America, the traditional millennia-old Ashkenazi rite has regained a strong following. Today the various sects and dynasties of Hasidic Judaism each use their own idiosyncratic version of Nusach Sfard.
Many Hasidic groups have slightly varying versions.
Nusach Maharitz, referring to and originating with Rabbi Yosef Tzvi Dushinsky, is the nusach used by most Dushinsky Hasidim. Their nusach is a mixture of nusach Ashkenaz and nusach Sefard, incorporating elements from both almost equally.