What food is Chicago (USA) famous for?

There are three classically, iconically, Chicago dishes, and one newcomer that is heavily associated with the city for serious foodies. Beyond that, as Mark Mayo notes, Chicago is a large, diverse, cosmopolitan city with a very large population of migrants from around the world, so there are any number of best-in-class eateries for a wide variety of cuisines - whatever might tickle your palate.

First off, for Chicago's traditional staples, you have:

• Chicago Style Deep Dish Pizza, as much as it pains me as a New Yorker to say this (It's a freakin' quiche at best dammit!), is pretty damned tasty, and is easily the dish most readily identified with the city by out of towners. The iconic places to pick one up are generally considered to be Uno's, Lou Malnotti's, and Gino's East, though asking a dozen Chicagoans will get you another dozen recommendations, as with the other items on this list.
• Chicago Hot Dogs are primarily notable for the wide variety of toppings. Hot Doug's is probably the most famous purveyor, though for a thick skinned tourist, a trip to The Wiener Circle might be more in order. (Warning: Link contains a great deal of profanity.)
• Italian Beef Sandwiches are the third member of the triumvirate, consisting of hot roast beef and peppers on an italian (submarine style) roll. You can find these in pizzeria's, sandwich shops, and delis all over town. Though sadly, I can't recommend a specific purveyor here.

Finally, for a more 'foodie' oriented option, Chicago has earned a reputation as a major hub for the budding style of Molecular Gastronomy. Several of the foremost chefs working with these sorts of advanced scientific cooking techniques are based out of Chicago, including Grant Achatz (Alinea, Next, Aviary), and Homaro Cantu (Moto).

Basically there are two dishes that the city is famous for.

• the deep-dish pizza - made with a soft dough, cheese slices, chopped tomato sauce and a variety of ingredients on top.
• Hot dogs are made of beef, steamed or boiled meat and served with mustard, onion, sweet sauce and pickled cucumbers, sliced tomatoes and salt, ketchup is not added.

However, Chicago's gastronomy is so diverse that it cannot be limited in any way, as though it has its own gastronomic traditions and a wide diversity of gastronomic cultures in the city, which includes Chinese, Greek, Jewish, Mexican, Polish, Ukrainian, Italian, Middle Eastern as well as the Ethiopian and Vietnamese to Peruvian cuisine.

Source - Typical food of Chicago, United States of America

Chicago-style pizza is one of the specialities (and in my humble opinion is well worth trying). It's very deep, and almost more like a pie than a pizza. You will struggle to get exactly this kind of pizza outside Chicago, and certainly outside the USA (whatever frozen-pizza manufacturers might like to claim). Uno Chicago Grill (formerly Pizzeria Uno) is probably the canonical restaurant for this, although there are competitors.

I had a cousin who was born and raised in Chicago and is currently having her holiday here in the Philippines. I got the chance to have a conversation with her just now; and asked her about this posted question in the forum related to where she is residing. I was told that there are three famous dishes in the city. These are the Chicago-style pizza, Chicago-style hot dog and the Chicago-style Italian beef sandwich.

I researched further and these are the things that I stumbled with while searching for great food that you can find in Chicago.

Chicago-style deep-dish pizza -It is called the deep-dish pizza because of its layer of high-sided dough that is formed in a special pan. The toppings and cheese are added like the regular pizza but the only difference is, the crust is most of the time 2-3 inches thick and gets slightly fried because of the oil in the pan.

Chicago-style hot dog -You can never go wrong with Chicago's hot dog. It's famous because of it's all-beef hot dog centered on a poppy seed bun, topped with mustard, relish, tomato, onions, a pickle spear, hot peppers and celery salt. The fun part is, you can create your own according to how you want it.

Chicago-style Italian Beef -A mouth-watering can make your day shine. Imagine an Italian roll with a tender roast beef bursting out with every bite. You have the option to order it hot ot sweet; dipped/wet, juicy or soaked. So no matter how you liked it, they can make it happen for you.