Use kuzu root starch.. It comes in rock-like granules. Mix 1 Tb kuzu with 1 Tb water first, then add to simmering chili until thickened. I use a lot of onions and peppers that give up a lot of water and kuzu works best! No change in flavor, texture or mouth-feel. Re-heats perfectly as original.

bigpan; That's a regional opinion. Texas chili doesn't have beans, but a lot of other regions do add them.

Wow, what a lot of different answers. After cooking competition chili for over 12 years, I can only add that the liquid is reduced by boiling/simmering, and, there are no beans in chili ! Just meat and spice. If a judge sees a piece of garlic or pepper it is rejected. (I used scored jalepenos and garlic in a cheesecloth bag, then removed before judging.)

I don't know why this came up again but if you have corn tortillas on hand, you can puree one in a blender with some of the liquid from the chile and pour it in and this will thicken it. Deborah Madison uses corn tortillas in a chilled zucchini cilantro soup that is delicious. This is similar to using masa or corn chips as others have suggested.

Yeah, I've never used flour in chili. Just take a good ladleful and blend or process, then add it back in. Try to get mostly solids in the ladle (beans, veg,, etc.). But if there's meat in it, avoid that. Pureed meat...no good.

toasted ground tortillas (masa)

I'll bet you a tamale what you've got at home is made from hominy. Hominy is made from corn but it's not the same thing; corn flour is different. Try to make a tortilla from a bag labeled "Corn Flour" and then tell me I'm wrong.

Masa = Dough (sometimes an abbreviation for Masa de Maíz but not to be confused with Masa de Trigo)
Hominy (Nixtamal) = Nixtamalized corn (from the Nahuatl word for "ashes")
Masa de Maíz = Dough made from hominy (despite the translation ambiguity)
Masa Harina = Dehydrated and powdered Masa de Maíz

Think of it how you will, hominy is substantially more nutritious, more flavorful and easier to digest than corn as it frees the niacin that would otherwise be trapped and removes the outer, indigestible hull. Hominy will form an elastic dough, corn flour will not.

I don't know what you'll accept as proof but here Rick Bayless describes the basics:

http://books.google.com/books?id=JMxLEsZYF2sC&pg=PA69#v=onepage&q&f=false

Here's how to make it yourself:

www.mexicoinmykitchen.com/2009/01/how-to-make-your-own-home-made-fresh.html

Sorry, but you're absolutely wrong. I have cooked with masa harina for years to make tamales and corn tortillas and have a big bag of it at home, and it's corn flour. The literal translation from Spanish to English for many words and phrases don't always reflect the actual meaning in Spanish. Masa may literally mean dough, but in Central and South America, when somebody says masa, it's short for masa de maíz. Just because most masa harina is made from hominy (a broken down corn product) doesn't mean that it's not corn flour. There's masa harina made from whole kernel corn as well, but both are corn flour. Ask anyone from Mexico, and they'll tell you the same thing. I could post multiple links providing proof, but I don't think that this site will let me do that.

Not that I don't agree with the above suggestions, note that masa harina (literally "dough flour") is not the same thing as corn flour. It is made from hominy (corn cooked in alkali and then hulled).

Also, unsweetened chocolate has more thickening power than sweetened versions, cocoa powder is even better.

Corn flour (masa harina) is the perfect thickener for chili. It has just the right texture and flavor. About two or three tablespoons added to a pot of chili while it's simmering will keep it from having the consistency of soup. Don't use cornstarch or cornmeal, because they have the wrong consistency, and wheat flour just doesn't taste right. Boiling off the excess liquid can take hours, dull the flavor, and cause the chili to stick to the bottom of the pot if not stirred regularly. Also, the consistency still won't be as good as using corn flour.

Cornstarch slurries will work initially, but will eventually break down and your chili will get watery again, especially if you reheat it. Masa harina (corn flour) is the best way that I know of, and you don't need much. Maybe 2 tablespoons per pot. You can find it in the grocery stores with the flour, it's used to make corn tortillas. Only problem is it's usually only sold in 5-pound bags. Some chili "kits" (pre-packaged seasoning mixes) include a small envelope of masa harina in them for this purpose. I've actually used regular white or yellow cornmeal when I haven't had masa harina. It works fine as well, and it won't turn it gritty or gluey since you use so little. If you have a mini food processor, give the corn meal a blitz in that to get a finer grain, and you'l essentially have masa harina.

Totally agree with drbabs; simmer it uncovered until enough liquid evaporates, and NEVER put flour in chili (or the chili police will come to your house and yell at you.) You might add a chunk of semisweet chocolate at the end, which will give it some heft. And make sure you've used enough chili powder!!! Don't be shy!!! .

I add crushed corn tortilla chips about 30 minutes before serving. They thicken the chili and add a nice toasted corn flavor - just be sure to undersalt the chili if you're using salted chips, then adjust the seasoning after the chips have been incorporated into the chili.

Instant mashed potato flakes thicken and don't really affect the taste although too much will counteract the spices.

Masa harina. You can stir it straight into the chili, and it works like a charm.

Lately I've been thickening things with a slurry made with cornstarch and a liquid used in the dish, or something that I just think will work well. I have used chicken broth, water, wine, and even some brandy. It really thickens things nicely with no floury or pasty taste. I put the cornstarch and the liquid in a small jar, shake it up well, and then add it ton the simmering pot. It thickens fairly quickly.

I use white cannelini beans - works every time.

You can also add some refried beans; those will thicken it while contributing to the flavor. It's a good way to use leftovers. I add about 1 cup refried beans to a medium pot of chili (maybe 8 cups total?).

I use corn flour - not corn meal because that tends to turn to polenta in the chili ... make sure to get the fine stuff like from Bob's Red Mill, and you can use beer to make a slurry which is also delicious!!!

Here's a link to a Cooks Country [America's Test Kitchen crew] Chili recipe that uses corn muffin mix as a thickener. I've used this trick and it worked pretty well. http://traceysculinaryadventures.blogspot.com/2010/01/chili-con-carne.html

If it's a chili that includes beans you can use a potato masher to pulp a portion and return to the pot and stir to incorporate.

Cooking chili uncovered for some time will cause the liquid to reduce and enable the chili to thicken. (Don't put flour in chili.)

Add some tomato paste.and let it simmer for a bit works every time. That is assuming that it is a tomato based chili, such as concarne.