Stir frying (Chinese: 炒; pinyin: chǎo; Wade–Giles: ch'ao³; Cantonese Yale: cháau) is a cooking technique in which ingredients are fried in a small amount of very hot oil while being stirred or tossed in a wok. The technique originated in China and in recent centuries has spread into other parts of Asia and the West. It is similar to sautéing in Western cooking technique.

Wok frying may have been used as early as the Han dynasty (206 BC – 220 AD) for drying grain, not for cooking. It was not until the Ming dynasty (1368–1644) that the wok reached its modern shape and allowed quick cooking in hot oil. However, there is research indicating that metal woks and stir frying of dishes were already popular in the Song dynasty (960–1279), and stir frying as a cooking technique is mentioned in the 6th-century AD Qimin Yaoshu. Stir frying has been recommended as a healthy and appealing method of preparing vegetables, meats, and fish, provided calories are kept at a reasonable level.

The English-language term "stir fry" was coined and introduced in Buwei Yang Chao's How to Cook and Eat in Chinese, first published in 1945, as her translation of the Chinese word chǎo 炒. Although using "stir fry" as a noun is commonplace in English, in Chinese, chǎo is used as a verb or adjective only.

Broadly speaking, there are two primary techniques: chao and bao. Both techniques use high heat, but chao adds a liquid and the ingredients are softer, whereas bao stir fries are more crispy because of the Maillard reaction.

The chao (炒) technique is similar to the Western technique of sautéing. There are regional variations in the amount and type of oil, the ratio of oil to other liquids, the combinations of ingredients, the use of hot peppers, and such, but the same basic procedure is followed in all parts of the country.

First the wok is heated to a high temperature, and just as or before it smokes, a small amount of cooking oil is added down the side of the wok (a traditional expression is 热锅冷油 "hot wok, cold oil") followed by dry seasonings such as ginger, garlic, scallions, or shallots. The seasonings are tossed with a spatula until they are fragrant, then other ingredients are added, beginning with the ones taking the longest to cook, such as meat or tofu. When the meat and vegetables are nearly cooked, combinations of soy sauce, vinegar, wine, salt, or sugar may be added, along with thickeners such as cornstarch, water chestnut flour, or arrowroot.

A single ingredient, especially a vegetable, may be stir fried without the step of adding another ingredient, or two or more ingredients may be stir fried to make a single dish. Although large leaf vegetables, such as cabbage or spinach, do not need to be cut into small pieces, for dishes which combine ingredients, they should all be cut to roughly the same size and shape.

Wok hei (simplified Chinese: 镬气; traditional Chinese: 鑊氣; Jyutping: wok⁶ hei³) romanization is based on the Cantonese Chinese pronunciation of the phrase; when literally translated into English, it can be translated as "wok thermal radiation" or, metaphorically, as the "breath of the wok". The phrase "breath of a wok" is a poetic translation Grace Young first coined in her cookbook The Wisdom of the Chinese Kitchen. In her book The Breath of a Wok, Young further explores the ideas and concepts of wok hei. An essay called "Wok Hay: The Breath of a Wok" explains how the definition of wok hei varies from cook to cook and how difficult it is to translate the term. Some define it as the "taste of the wok," a "harmony of taste," etc.: "I think of wok hay as the breath of a wok—when a wok breathes energy into a stir fry, giving foods a unique concentrated flavor and aroma."