Sh'mini Atzeret and Simchat Torah: History

Simchat Torah or Simḥath Torah (also Simkhes Toreh,   "Rejoicing with/of the Torah,") is a celebration marking the conclusion of the annual cycle of public Torah readings, and the beginning of a new cycle. Simchat Torah is a component of the Biblical Jewish holiday of Shemini Atzeret ("Eighth Day of Assembly"), which follows immediately after the festival of Sukkot in the month of Tishrei (mid-September to early October on the Gregorian calendar).

Simchat Torah begins at sundown on Mon, 05 October 2015.

Sh’mini Atzeret, Hebrew for “eighth-day convocation,” is the name given to the eighth day of Sukkot.  Leviticus 23:36 proclaims: “On the eighth day you shall observe a holy convocation.” Jews in biblical times observed Sukkot for seven days. For them, this eighth day came after Simchat Torah; for Orthodox, Conservative, and many Reform Jews today, it is the last day of the Simchat Torah festival.

Sh’mini Atzeret was originally a time of reflection on the holy days of Sukkot, which had just ended. Jews who left the booths they had occupied throughout Sukkot engaged in a final day of prayer before returning to their daily routine. Over time, Sh’mini Atzeret also became a day on which Jews recited a special prayer for rain in the year to come – quite appropriate in view of Simchat Torah’s agricultural motif. The eighth day of Sukkot, Sh’mini Atzeret, is traditionally a separate festival in its own right. In Reform congregations, which generally observe one day of holidays, rather than two, Sh’mini Atzeret is observed concurrently with Simchat Torah, the festival of “Rejoicing in the Torah.”

Simchat Torah celebrates the end (and the beginning) of the annual Torah-reading cycle.  Just as we reach the concluding section of Deuteronomy (the fifth book of the Torah) do we start over once again with Genesis (the first book of the Torah).

Only in the 11th century did the 9th day after the beginning of Sukkot take on both the name and the festive ritual of what we now recognize as Simchat Torah. An annual holiday of this nature implies a one-year cycle of Torah reading, but such was not always the case. In ancient Palestine, Jews followed a triennial, or three-year, cycle of Torah reading. The one-year cycle was a custom of the Babylonian Jewish community. It was not until the 8th century that the great majority of Jews adopted the annual system. Simchat Torah as an annual observance, then, emerged only after the divergence in customs over the Torah reading cycle was resolved.

Simchat Torah is a joyous celebration during which the Torah scrolls are taken from the ark and carried by congregants around the synagogue seven times. During these seven circuits, or hakafot, those not carrying Torahs often will wave brightly colored flags and sing Hebrew songs.

In Israel, Simchat Torah is observed on the one and only day of Sh’mini Atzeret, but for most Israelis it is just another day of Sukkot vacation. In many towns, public celebrations are held on the night after Simchat Torah.  Known as hakafot shniyot (second processions), these events are simulations of Simchat Torah dancing and singing, but with professional musicians and electronic amplification. They are, in effect, "reruns" of Simchat Torah, designed to allow the public to enjoy the holiday without any of the restrictions or accoutrements of religion. These public festivals are usually popular and crowded. 

FROM: http://www.reformjudaism.org/shmini-atzeret-and-simchat-torah-history