Zhangjiakou is a city in the Hebei Province of northern China. It has a population of 4.3 million, and covers 36,947 square kilometers. Zhangjiakou's mayor is Zheng Xuebi.

The water-scarce city was historically the chief northern gate in the Great Wall to China for Europeans travelling along the Tea Road (such as Nicolae Milescu).

In the 19th century, the town was the seat of a very extensive transit trade. In early autumn long lines of camels would come in from all quarters for the conveyance of the tea chests from Zhangjiakou, the Kalgan, to Kyakhta; and each caravan usually made three journeys in the winter. Some Russian merchants had permanent residences and warehouses just outside the gate.

In October 1909, Kalgan was connected by railway with Peking. The 1911 Encyclopaedia Britannica noted that, in Kalgan, "the ordinary houses have an unusual appearance, from the fact that they are mostly roofed with earth and become covered with green-sward" and that "on the way to Peking the road passes over a beautiful bridge of seven arches, ornamented with marble figures of animals".

In the early 1960s at the height of Sino-Soviet tensions, Zhangjiakou was considered one of the most important cities in China for military strategy reasons. Zhangjiakou was aptly nicknamed, "Beijing's Northern Door", because whoever controlled Zhangjiakou was in a good position to either attack (in the case of the Soviets) or defend (in the case of the Chinese) Beijing.