The history of responsa in Judaism (Hebrew: שאלות ותשובות; Sephardic: She'elot Utshuvot; Ashkenazic: Sheilos Utshuvos;, usually shortened to שו"ת Shu"t ), spans a period of 1,700 years. Rabbinic responsa constitute a special class of rabbinic literature, differing in form, but not necessarily in content, from Rabbinic commentaries devoted to the exegesis of the Bible, the Mishnah, the Talmud, and halakha (the codes of Jewish religious law). The codes themselves contain the rules for ordinary incidents of life. The responsa literature covers all these topics and more.<ref name="Jewish">Jewish Encyclopedia bibliography: Responsal literature as a whole has as yet found no literary historian; single periods have been discussed while others have been entirely neglected, the works on these separate epochs including: Joel Müller, Briefe und Responsen aus der Vorgaonäischen Jüdischen Literatur, Berlin, 1886; idem, Einleitung in die Responsen der Babylonischen Geonen. ib. 1891; Zecharias Frankel, Entwurf einer Geschichte der Literatur der Nachtalmudischen Responsen, Breslau, 1865. The responsa by European and American rabbis to problems arising in America are summarized by J. D. Eisenstein, The Development of Jewish Casuistic Literature in America, Baltimore, 1905.</ref> The mode, style and subject matter have changed as a function of the travels of the Jewish people and of the development of other halakhic literature, particularly the codes. Forumulation of responsa, or she'elot ve-t'shuvot, which literally translates to questions and answers, generally involve an individual or group asking either teachers, rabbis, or heads of yeshivot about halakhah (Jewish law) and the party responding via an exchange of letters. Responsa literature spans 1700 years and there are even responsa being developed based on questions posed today. The development of responsa literature can be divided into four periods: the Tannaitic Period, the Geonic Period, the First Rabbinic Epoch, the Second Rabbinic Epoch, the Third Rabbinic Epoch, and the Fourth Rabbinic Epoch. Talmudic era The responsa of the first five centuries are not contained in special works; they are scattered through the writings of both Talmuds (the Babylonian Talmud and the Jerusalem Talmud). Works devoted especially to responsa first appear in the post-Talmudic period. Many responsa have been lost, but those extant number hundreds of thousands, in almost a thousand known collections. Pre-Mishnaic era No responsa are known to exist from before the Mishnah (200 CE); it is doubtful whether any were written before this period. A tradition held that no halakha (law) should be written down (see Oral Torah). Even