This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by others.
The current definition of the Hebrew calendar is generally said to
have been set down by the Sanhedrin president Hillel II in
approximately AD 359. The original details of his calendar are,
however, uncertain.
The Hebrew calendar is used for religious purposes by Jews all over
the world, and it is the official calendar of Israel.
The Hebrew calendar is a combined solar/lunar calendar, in that it
strives to have its years coincide with the tropical year and its
months coincide with the synodic months. This is a complicated goal,
and the rules for the Hebrew calendar are correspondingly
fascinating.
 
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