Kitniyot, (Hebrew: קִטְנִיּוֹת ,קיטניות, qit'niyyot) (legumes) is a category of foods that may not be eaten during Passover by Jews following traditional Ashkenazi laws and customs. Long-standing tradition in other communities and recent rulings have given support in certain cases for variation from this practice.
Kitniyot are legumes such as rice, corn, soy beans, string beans, peas, lentils, mustard, sesame seeds and poppy seeds.
Laws and customs 
The Torah (Exodus 13:3) prohibits Jews from eating chametz during Passover. Chametz is only leaven made from the "five grains": wheat, spelt, barley, shibbolet shu'al (two-rowed barley, according to Maimonides; oats according to Rashi) or rye. There are additional rabbinic prohibitions against eating these grains in any form other than matzo.
Among Ashkenazi Jews, the custom (Minhag) during Passover is to refrain from not only products of the five grains but also other grains and legumes. Traditions of what is considered kitniyot vary from community to community but generally include maize (North American corn), as well as rice, peas, lentils, and beans. Many also include other legumes, such as peanuts and soy, in this prohibition. The Chayei Adam considers potatoes not to be kitniyot, and decided that because potatoes were unknown in the time when the prohibition was created they could not have been included in the prohibition (Sha'arei Teshuvah 453:1). This opinion is followed by nearly all Ashkenazi authorities. Sephardi Jews typically do not observe the ban on kitniyot, albeit some groups do abstain from the use of dried pulses during Passover.
The origins of this practice is not clear, though two common theories are that these items are often made into products resembling chametz (e.g. cornbread), or that these items were normally stored in the same sacks as the five grains and people worried that they might become contaminated with chametz. It is also possible that crop rotation would result in the forbidden chametz grains growing in the same fields, and being mixed in with the kitniyot. Those authorities concerned with these three issues suggested that by avoiding eating kitniyot, people would be better able to avoid chametz. Vilna Gaon (Hagaos HaGra, ibid.) proposes a different source for this custom. The Gemara in Pesachim (40b) notes that Rava objected to the workers of the Exilarch cooking a food called chasisi on Pesach, since it was wont to be confused with chametz. Tosafot understand that chasisi are lentils, and thus, argues Vilna Gaon, establishes the basis for the concern for kitniyot. Rabbi David Golinkin in the Responsa of the Masorati (Conservative) Movement cites Rabbenu Manoah (Provence, ca. 1265) who wrote an opinion in his commentary on Maimonides (Laws of Festivals and Holidays 5:1) that "It is not proper to eat kitniyot on holidays because it is written (in Deuteronomy 16:14) that ‘you shall rejoice in your festivals’ and there is no joy in eating dishes made from kitniyot".
Jewish law is quite stringent about the prohibition against chametz in the house during Passover, even in small amounts. Thus a tradition developed to avoid these products altogether.
Even where the prohibition against kitniyot was practiced, some poskim opposed it, among them Rabbi Yeruham of 14th century Provence  Others, including Rav Moshe Feinstein did not advocate abandoning the custom, but he opposed expanding the list of forbidden kitniyot 
Rabbi David Bar-Hayim of Machon Shilo asserts that consuming kitniyot is permissible for Ashkenazim in the Land of Israel  According to the Forward, some Israelis are choosing a more permissive rabbinical interpretation of kitniyot, which allows for the consumption of a wider range of formerly banned items.
Maxwell House coffee hired the Joseph Jacobs advertising firm in the 1930s to market to a Jewish demographic. The agency hired a rabbi to research coffee, resulting in a determination that the coffee bean is more like a berry than a bean, thus making it kosher for Passover.
- "קִטְנִיּוֹת" (in Hebrew). Morfix. Retrieved March 31, 2013.
- Plea for Kitniyot, Jerusalem Post
- Mathes-Scharf, Arlene. "Why is This Food Different from Other Foods? Kashrus/Passover and Modern Food Processing". Kashrut.com. Retrieved March 27, 2013.
- Golinkin, "The Kitniyot Dilemma, Kolot Vol 6, No. 3, page 10, Spring 2013
- Igrot Moshe, Orah Hayyim 3. 63
- English Article and Hebrew Legal Ruling
- OU Kitniyot Kosher for Passover Supervision Accessed 2011 March 24
- Berger, Joseph (April 8, 2011). "Giving a Haggadah a Makeover". The New York Times. Retrieved March 23, 2013.