Qimen Dunjia is an ancient Chinese divination system that integrates knowledge from the Book of Changes, astronomy, calendars, Yin and Yang, and the Five Elements. It is known as one of the "Three Ancient Forms" along with Liuren and Taiyi, and ranks first among them. It was hailed by the ancients as "the study of emperors," and was used not only for military strategy and troop deployment but also for predicting auspiciousness or inauspiciousness, and selecting auspicious days and times.

Its name consists of three parts:
Qi: Refers to the "Three Qis" - Yi (Day Qi), Bing (Month Qi), and Ding (Star Qi), symbolizing auspicious qi;
Gate: Refers to the "Eight Gates" - Xiu, Sheng, Shang, Du, Jing, Si, Jing, and Kai, representing human affairs and directions, among which "Kai, Xiu, and Sheng" are the three auspicious gates;
Dùnjiǎ: "Dùn" means "hide", and "jiǎ" is the first of the ten heavenly stems, symbolizing the commander or core force. Because jiǎ is afraid of the metal of gēng, it is "hidden" under the six symbols (wǔ, jǐ, gēng, xīn, rén, guǐ), forming a layout structure.
Qi Men Dun Jia involves setting up a layout at a specific time, combining elements such as the heavenly, earthly, human, and divine spheres into a nine-palace and eight-trigrams pattern, to analyze spacetime energy and determine the auspiciousness or inauspiciousness of situations. Traditionally, those proficient in Qi Men Dun Jia are believed to possess the ability to "understand astronomy in the sky, observe geography on the earth, and comprehend human affairs in the midst," thus possessing extremely high strategic and predictive value.
Historically, it is said to have originated from Huangdi, and was passed down through Jiang Taigong, Zhang Liang