Hexie (Chinese: 和谐号; pinyin: Héxié hào; lit. 'Harmony'), also known as the CRH series EMU, is an umbrella term for the multiple unit high-speed and higher-speed trains operated by China Railway under the China Railway High-speed brand. All series of Hexie are based on foreign-developed technology and later manufactured locally in China through technology transfer licenses, with the ultimate goal of China acquiring the know-how and capability to produce high-speed rail trains.

The Harmony series does not belong to any single platform, instead encompassing all high-speed trains in China with roots in foreign technology, specifically CRH1, CRH2, CRH3 and CRH5. Although later variants of Hexie such as CRH380A were designed by Chinese companies, they are still classified as CRH due to incorporation of foreign technology.

In 2007, China's Ministry of Railways drafted a plan for China's future high-speed network. Bombardier Transportation, Kawasaki Heavy Industries, Alstom and later Siemens joined the high-speed train manufacturing project that later became known as Harmony. Forming joint-ventures with Chinese company CNR and CSR, these four foreign companies signed agreements with China to manufacture high-speed trains for China as well as provide assistance for Chinese companies to manufacture train cars locally in the future.

While the initial train sets from each Hexie series were manufactured overseas, subsequent sets are manufactured locally through technology transfer, a key requirement for China. The signalling, track and support structures, control software, and station design are developed domestically with foreign elements as well. Although the first domestically produced trains were initially delivered in complete knock-down form, eventually manufacturing as a whole became predominantly Chinese.

China currently holds many patents related to the internal components of these trains, re-designed in China to allow the trains to run at higher speeds than the foreign designs allowed. However, these patents are only valid within China, and as such hold no international power. This weakness on the intellectual property of Hexie trains became an obstruction for China to export its high-speed rail related products, leading to the development of a completely redesigned train brand, Fuxing, which is based on indigenous technologies.

While most Hexie series trains are designed for China Railway, a variant of the CRH380A has been modified for operation by MTR Corporation of Hong Kong, who will operate these trains under the brand Vibrant Express specifically for the Guangzhou–Shenzhen–Hong Kong Express Rail Link.

The Harmony brand has different electric multiple unit trainsets, the designs for which are imported from other nations and designated CRH-1 through CRH-5 and CRH380A(L), CRH380B(L), and CRH380C(L). CRH trainsets are intended to provide fast and convenient travel between cities. Some of the trainsets are manufactured locally through technology transfer, a key requirement for China. The signalling, track and support structures, control software, and station design are developed domestically with foreign elements as well, so the system as a whole is predominantly Chinese. China currently holds many new patents related to the internal components of these trains, re-designed in China to allow the trains to run at higher speeds than the foreign designs allowed. However, these patents are only valid within China, and as such hold no international power.

The trainsets are as follows: