3G / TD-SCDMA (Time Division Synchronous Code Division Multiple Access) is a mobile telephone standard for wireless network operators who want to move from a second generation (2G) wireless network to a third-generation (3G) one. Supporting data transmission at speeds up to 2 Mbps, TD-SCDMA combines support for both circuit-switched data, such as speech or video, and also packet-switched data from the Internet. The standard combines time division multiple access (TDMA) with an adaptive, synchronous-mode code division multiple access (CDMA) component.

However, the proponents of TD-SCDMA also claim that it is better suited for densely populated areas. Further, it is supposed to cover all usage scenarios, whereas W-CDMA is optimised for symmetric traffic and macro cells and TD-CDMA is best used in low mobility scenarios within micro or pico cells.

TD-SCDMA is an air interface found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA. Together with TD-CDMA, it is also known as UMTS-TDD or IMT 2000 Time-Division (IMT-TD).

TD-SCDMA is being pursued in the People's Republic of China by the Chinese Academy of Telecommunications Technology (CATT), Datang and Siemens AG, in an attempt not to be dependent on Western technology. This is likely primarily for practical reasons, other 3G formats require the payment of patent fees to a large number of Western patent holders. TD-SCDMA is based on spread spectrum technology which makes it unlikely that it will be able to completely escape the payment of license fees to western patent holders.