Zhangjiakou, also known also by several other names, is a prefecture-level city in northwestern Hebei province of North China, adjacent to Beijing to the southeast. Its administrative area has a population of 4.35 million, and covers 36,947 square kilometres (14,265 sq mi). The urban area of Zhangjiakou is divided into Qiaoxi and Qiaodong Districts which have 473,193 inhabitants in 2010, but the prefecture-level city is much larger, spanning around 36,800 square kilometres (14,200 sq mi).

Zhangjiakou is written 张家口 in simplified Chinese and 張家口 in traditional Chinese. It is Zhāngjiākǒu in pinyin and the name means "Zhang family gate." Older names for the town in Chinese include Zhāngyuán (張垣), used in the Republican era, and Zhāngjiābǎo (張家堡).

Zhangjiakou was historically known to the Europeans as Kalgan until the mid 20th century. This name derives from the Mongolian name of the city, , "Chuulalt haalga" or shorter, , "haalgan" which means "the gate" (in the Great Wall). In Manchu, the city is known as (Imiyangga jase).