The Etrog is used with the Lulav, Hadas (myrtle) and willow branch (Arava) at the Feast of Tabernacles, or Sukkot . Of the Four Species of plants enumerated in Leviticus xxiii. 40, on which the carrying of the lulav is based, tradition takes "the fruit of the goodly tree" (, properly "the fruit of a fair or noble tree") to designate the citron. The Arabic name for the fruit, itranj اترنج is cognate with the Hebrew. The itranj is mentioned favorably in the hadith.

The citron (κίτρον, κίτριον); Citrusfruit of a tree of the orange and lemon family. It is oblong in shape, and sometimes as much as six inches in length. The skin is thick, somewhat hard, fragrant, and covered with protuberances; the pulp is white and subacid. Modern naturalists assume the north of India to be its native home; but it passed to the countries of the Mediterranean from Media or Persia ; hence the name of the tree, "Citrus medica," and of the fruit, "Malum medica," or "Malum Persica"

It is therefore possible that the Jews brought the tree with them from Babylonia to Eretz Yisrael on their return from the Babylonian Captivity.

Based on content from 1901-1906 Jewish Encyclopedia. Please update as needed.