- The Ashkenazic minhag is to avoid eating Kitniyot on Pesach, however, even Ashkenazim hold that one does not have to burn or sell one's Kitniyot.  One is permitted to keep Kitniyot in one's home on Pesach.
- Although some sephardic poskim say that it is preferable not to eat kitniyot, the custom among Sephardim is to eat kitniyot on Pesach. 
Which foods are Kitniyot?
- The earlier Poskim mention that rice, buckwheat/kasha, millet, beans, lentils, peas, sesame seeds and mustard are included in the minhag 
- Among traditional Ashkenazi Jews, the custom during Passover is to refrain from not only products of the five grains but also kitniyot, such as 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 peanuts in this prohibition, and one source, the Chayei Adam, also includes potatoes in his list, although his opinion is not followed by any large or major groups.
- Some common foods that are Kitniyot include: Beans, Black eye peas, Buckwheat, Canola oil, Chickpeas, Coriander, Corn, Fenugreek, Kasha, Lentils, Mustard, rapeseed oil,Peanuts , Rice, Sesame seeds, String Beans, Sunflower seeds 
- On the other hand, potatoes (see below), coffee, tea, garlic, nuts, radishes and olives and not treated as kitnios 
- Some say that quinoa is kitniyot, however, if there's a medical issue one may be lenient to use it on Pesach. 
Reason for prohibition
- From the Torah, only the five grains can become chametz and not legumes or rice. 
- The Smak (Rabbi Yitzchak of Korbol) explains that products of kitniyot appear like chametz products. For example, it can be hard to distinguish between rice flour (kitniyot) and wheat flour (chametz). Therefore, to prevent confusion, all kitniyot was prohibited.
- The Beit Yosef (Rabbi Yosef Karo, 16th century, Israel) notes that since regular grains may become mixed together with kitniyot (apparently due to changes in crop cycles), one may inadvertently come to eat actual chametz.
- The origins of this practice are 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 was also possible that crop rotations 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. The Vilna Gaon (Hagaos HaGra, 453) indeed actually cites a novel source for this custom. The Gemorrah in Pesachim (40b) notes that Rava objected to the workers of the Raish Gelusa (the Exilarch) cooking a food called chasisi on Pesach, since it was wont to be confused with chametz. The Tosefos explain that, according to the Aruch, chasisi are lentils, and thus, argues the Gra, establishes the basis for the concern of kitniyot.
Halachot of kitniyot
- The minhag to not eat kitnios begins on Erev Pesach at the same time that one may not eat chametz . Although one may not eat kitnios, one may own and derive benefit from kitnios. Therefore, on Pesach one may keep cans of sweet corn in their property or feed millet to their parrot. Additionally, children, people who are ill, and people whose diet is otherwise restricted and must eat kitnios, are excluded from the minhag and may do so after consulting with a Rav. This halacha is quite relevant to baby formulas and nutritional supplements (e.g. Ensure) which invariably contain kitnios, and are usually used by people who have few non-kitnios choices, if any. When such foods are used on Pesach they should be prepared in special non-Pesach and non-chametz utensils, which should not be washed with the Pesach dishes. 
- It is permitted even for Ashkenazim to eat Kosher for Pesach foods that were made in pots that were used for cooking kitniyot if it wasn't used within 24 hours. Some say that it is permitted even if it was used within 24 hours. 
- Kitnios is batel b’rov, which means that if someone accidentally put kitnios into their Pesach food, the food is b’dieved permitted assuming the food contains more non-kitnios than kitnios . This means that although the food may have a pronounced taste of kitnios, the food is permitted (unless there are recognizable pieces of kitnios which haven’t been removed). Therefore, if a beverage is sweetened with aspartame made of kitnios shenishtaneh, even those people who hold that aspartame is forbidden (as explained above) may drink the beverage because the aspartame is batel b’rov in the other ingredients. Similarly, we have seen that there is a disagreement as to whether fenugreek is kitnios. Nonetheless, even those who follow the strict approach may consume maple syrup which is flavored with fenugreek (as it often is) because it is batel b’rov. Thus, although we’ve seen a number of disagreements as to whether certain foods are or aren’t kitnios, those disagreements are limited to one who wants to consume the actual item (or a hashgachah certifying someone else who is intentionally putting the ingredient into a food), but these disagreements rarely affect consumers. 
- Some say that new tablecloths which may have been ironed with clothing starch, which could be made from Kitniyot, should be laundered in hot water in order to remove the starch. 
- Some poskim say that if a sephardi wants to eat kitniyot but his custom earlier was not to then he should perform a hatarat nedarim. 
- Background: The Gemara Pesachim (35a) writes that Chametz includes foods made with the five grains. See the Wheat and Grain Products page about the precise definition of the five grains. The says that orez and dochen (Tosfot Brachot 37a translates rice and millet) are not chametz since when used to produce bread doesn't ferment. The Rambam (Chametz UMatzah 5:1) rules that there's no issue of chametz with grains other than the five grains, such as rice, millet, or beans. Furthermore, says the Rambam, even if one were to mix those grains with hot water and make dough that rises, it is permitted since that's considered rotting and not positive fermentation.
- The Tur 453:1 writes that the minhag of his location was not to eat kitniyot on Pesach. The Rabbenu Yerucham (cited by the Beit Yosef 453:1), Rabbenu Yechiel (cited by Beit Yosef 453:1), and Shulchan Aruch 453:1 agree.
- The Smak (cited by the Beit Yosef 453:1) explains that the minhag not to eat kitniyot on Pesach is concerned that perhaps a person will be confused between a bread or cooked dish made from kitniyot and one made from the five grains. Additionally, kitniyot flour sometimes has flour of the five grains mixed in. The Darkei Moshe 453:1, codified in the Rama 453:1, writes that the Ashkenazic minhag is to not to eat kitniyot on Pesach and one shouldn't deviate from the minhag.
- The Shulchan Aruch 453:1 writes that it is permitted to eat a cooked dish made out of Kitniyot. The Rama 453:1 writes that the minhag Ashkenaz was to forbid and one shouldn't change this minhag. This is quoted by ashkenazic poskim including Darchei Moshe 453:2, Levush 453:1, Chayei Adam 127:1, Aruch Hashulchan 453:4, Elya Rabba 453:3, Prisha 453:3, Kitzur S:A, Daat Torah page 119. see also Yechave Daat 1:9 and 5:32 as well as Kaf Hachaim 453:11. Aruch Hashulchan 453:4 says that being lenient in this minhag is testimony that one does not fear Hashem or fear sin, and does not understand the ways of torah.
- This minhag is found in several rishonim with several different reasons.
- Firstly, there are some rishonim who thought that there was insufficient reason to follow this minhag of not eating kitniyot. Rabbenu Yerucham 5:3 and Tur 453:1 think that this minhag is overly stringent and difficult to understand.
- Hagahot Maimoniyot (cited by Beit Yosef 453:1) writes that there's a minhag not to eat kitniyot such as beans and lentils because it is possible to make cooked dishes from them just like grains. Also, grains are sometimes mixed up with kitniyot. He adds that mustard is also included in the minhag since it is similar to a grain. Mordechai Masechet Pesachim 2:588 cites this as well in name of the Smak. The Agur (no. 845) records a minhag not to eat kitniyot, rice, and millet since grain was sometimes mixed in.
- Rama 453:1
- Rav Pealim 3:30, Yechave Daat 1:9 and 5:32.
- Beis Yosef O.C. 453, Rema 453:1 & 464:1 and Mishna Brurah 453:4, 7 & 11
- Mishna Brurah 453:4
- see, however, https://oukosher.org/passover/guidelines/food-items/kitniyot-list/
- Avnei Nezer OC 533
- Iggeros Moshe (O.C. 3:63) assumes that peanuts are not kitnios but notes that some have a custom to be machmir. Kashrut.com includes it as kitniyot.
- Kashrut.com writes that the above mentioned foods are considered Kitniyot. For a full list of Kitniyot, see Kashrut.com.
- Sha’arei Teshuvah 453:1, Chayei Adam 127:7. Pri Megadim Eshel Avraham 464:1 writes that he doesn't understand why some people don't eat garlic on Pesach but nevertheless one should be stringent.
- Rav Yisrael Belsky on OU Pre-Pesach Webcast 5769 between minutes 23 and 24 and on OU Pre-Pesach Webcast 5771 between minutes 101:30 and 103:30. Rav Moshe Feinstein did not advocate abandoning the custom, but he opposed the tendency to expand the list of forbidden kitniyot (see Igrot Moshe, Orah Hayyim 3. 63).
- The Gemara (Pesachim 35a) states that one may only fulfill one's obligation of matza on Pesach with matza made from the five grains. The gemara explains that since the Torah contrasts Matza and chametz, anything which could ferment and become chametz may be used for matza, which is only the five grains and not rice or millet. See Pesachim 114b for a proof that the Amoraim ate rice on Pesach. The Rambam (Chametz UMatza 5:1) and Shulchan Aruch 453:1 codify this gemara. See Bet Yosef 453:1 for more background of this issue.
- Shevet HaLevi III:31 citing Chok Yaakov 471:2, Rav Elyashiv quoted in Siddur Pesach Kihilchato 16:footnote 42
- Based on the Mishna Brurah 453:9 who says that kitniyot is nullified with a majority, the Yechave Daat 5:32 writes that vessels in which kitniyot was cooked are permitted for Ashkenazim even within 24 hours. Az Nedberu 8:20:4 and Banim Chavivim (Siman 17, p. 415-9) agree. Az Nedberu 8:20:4 writes that an Ashkenazi shouldn't avoid lending his pots to a Sephardi on Pesach. Rabbi Hershel Schachter in a shiur on yutorah.org (min 37-40) explains that something that is only forbidden because of a minhag, there's no rabbinic prohibition of not using a pot after 24 hours, therefore if one cooked kitniyot in a pot one may use it after 24 hours has passed.
- Rema 453:1 as per Mishna Brurah 453:9, Pri Chadash 453:1, Elya Rabbah 453:4, Shulchan Aruch Harav 453:5, Chayei Adam 127:1, Az Nedberu 8:20:4.
- Nitei Gavriel (Pesach 77:17)
- Haggadah of Rav Elyashiv page 12