You shall count for yourselves -- from the day after the Shabbat, from the day when you bring the Omer of
count, fifty days... -Leviticus 23:15-16

You shall count for yourselves seven weeks, from when the sickle is first put to the standing crop shall you
begin counting seven weeks. Then you will observe the Festival of Shavu'ot for the L-RD, your G-d
-Deuteronomy 16:9-10

According to the Torah (Lev. 23:15), we are obligated to count the days from Passover to Shavu'ot. This
period is known as the Counting of the Omer.  An omer is a unit of measure.  On the second day of
Passover, in the days of the Temple, an omer of barley was cut down and brought to the Temple as an
offering.  This grain offering was referred to as the Omer.

Every night, from the second night of Passover to the night before Shavu'ot, we recite a blessing and state
the count of the omer in both weeks and days.  So on the 16th day, you would say "Today is sixteen days,
which is two weeks and two days of the Omer."  The Orthodox Union has a chart that provides the
transliterated Hebrew and English text of the counting day-by-day.

The counting is intended to remind us of the link between Passover, which commemorates the Exodus, and
Shavu'ot, which commemorates the giving of the Torah.  It reminds us that the redemption from slavery
was not complete until we received the Torah.

This period is a time of partial mourning, during which weddings, parties, and dinners with dancing are not
conducted, in memory of a plague during the lifetime of Rabbi Akiba.  Haircuts during this time are also
forbidden.  The 33rd day of the Omer (the eighteenth of Iyar) is a minor holiday commemorating a break in
the plague.  The holiday is known as
Lag b'Omer.  The mourning practices of the omer period are lifted
on that date.  The word "Lag" is not really a word; it is
the number 33 in Hebrew, as if you were to call the
Fourth of July "Iv July" (IV being 4 in Roman numerals).  See Hebrew Alphabet for more information about
using letters as numbers.

There was at one time a dispute as to when the counting should begin.  The Pharisees believed that G-d
gave Moses an oral Torah along with the written Torah, and according to that oral Torah the word
"Shabbat" in Lev. 23:15 referred to the first day of Passover, which is a "Shabbat" in the sense that no
work is permitted on the day (Rosh Hashanah and Yom Kippur are both referred to as "Shabbat" in this
sense, though they cannot both occur on a Saturday in the same year; see Lev. 23:24 and 23:32; see also
Lev. 23:39 the first and eight days of Sukkot are called "Shabbat"). In this view, held by most Jews today,
the counting begins on the second night of Passover, that is, the day after the non-working day of
Passover.  The Tzedukim (Sadducees) rejected the idea of an oral Torah and believed that the word
"Shabbat" in Lev. 23:15 referred to the Shabbat of the week when Pesach began, so counting would
always begin on a Saturday night during Passover.  The Sadducees no longer exist; today, only a small
sect call the Karaites follow this view.

List of Dates
Lag B'Omer will occur on the following days of the Gregorian calendar:

Jewish Year 5769: sunset May 11, 2009 - nightfall May 12, 2009
Jewish Year 5770: sunset May 1, 2010 - nightfall May 2, 2010
Jewish Year 5771: sunset May 21, 2011 - nightfall May 22, 2011
Jewish Year 5772: sunset May 9, 2012 - nightfall May 10, 2012

Lag B'Omer
The Counting of the Omer