A takkanah (Hebrew: תקנה, romanized: taqqānā, plural takkanot) translated as 'improvement', is a major legislative enactment within halakha, the normative system of Judaism's laws.
Takkanot were enacted even in the time of the Second Temple, those of unknown origin being ascribed to earlier leaders, and they have been promulgated at all subsequent periods of Jewish history.
These gezeirot are executed out of fear that some might otherwise carry the mentioned items between home and the synagogue, thus inadvertently violating one of the 39 Melakhot, a greater sin than neglecting the banned mitzvah.
[1] Ascribed to Moses: To Joshua: To Boaz, the ancestor of David: To King David: To King Solomon: To the early prophets: To the Prophets before the destruction of Solomon's Temple: To the Prophets after the destruction of the Temple: To Ezra: To the men of the Great Assembly: Ascribed to John Hyrcanus (135-106 BC): By the court of the Hasmoneans: By the priestly court: By Shimon ben Shetach: By Hillel the Elder (75 BC - 5 AD): By Gamaliel I (mid-1st century): Most of the ordinances of Yohanan ben Zakkai were promulgated before the time of the destruction of the Temple in Jerusalem.
When Hadrian issued his decree forbidding the Jews to observe their religion, the teachers, including R. Akiba, R. Tarfon, and R. Jose the Galilean, met in council and agreed that during the time of the persecution the Law might be transgressed in all respects, except as regarded the commands relating to idolatry, chastity, and morality, although this regulation was observed only superficially and only when necessary in order to deceive the Roman spies.
These include: The making of new ordinances did not end with the completion of the Mishnah: enactments were promulgated also in the Amoraic, Saboraic, and Geonic periods of Jewish law, although their exact dates are no longer known.
Examples of takkanot issued by the Conservative Movement in modern times include allowing women to count in a minyan and to serve as witnesses to a beth din, as well as removing restrictions on kohen marriage.