A casserole, from the French word for "saucepan",is a large, deep dish used both in the oven and as a serving vessel. The word is also used for the food cooked and served in such a vessel, with the cookware itself called a casserole dish or casserole pan.

Casseroles in the United States or continental Europe usually consist of pieces of meat (such as chicken) or fish (such as tuna), various chopped vegetables, a starchy binder such as flour, potato or pasta, and, often, a crunchy or cheesy topping.Liquids are released from the meat and vegetables during cooking, and further liquid in the form of stock, wine, beer (for example lapin à la Gueuze), gin, cider, or vegetable juice may be added when the dish is assembled. Casseroles are usually cooked slowly in the oven, often uncovered. They may be served as a main course or a side dish, and may be served in the vessel in which they were cooked. In the United Kingdom, Australia, and New Zealand, a casserole is named for its dish, rather than its contents. Casseroles in these countries are very similar to stews. The difference is that once the meat and vegetables are browned on top of the stove, they are then cooked in liquid in the oven, in a closed dish, producing meat that is tender and juicy, from long slow cooking. As the heat is indirect, there is also less chance of it burning.

Types of casserole include ragout, hotpot, cassoulet, tajine, moussaka, lasagne, shepherd's pie, gratin, rice or macaroni timballo, and carbonnade. A distinction can be made between casseroles and stews: stewing is a cooking process whereby heat is applied to the bottom of the cooking vessel (typically over a fire or on a stove), whereas casserole cooking is generally done in an oven to bake where heat circulates all around the cooking vessel. Casseroles may be cooked covered or uncovered, while braises are typically covered to prevent evaporation.