It begins on the 25th day of Kislev in the Hebrew calendar, which can fall anywhere between late November and late December in the Gregorian calendar. It will begin on November 28 this year. For eight days, the celebration is marked by some rites.
Hanukkah is an eight-day celebration of lights commemorating the Maccabean insurrection against the Seleucid Empire in the second century BC when Jerusalem was recaptured and the second temple was rededicated.