CDMA2000 (also known as IMT Multi‑Carrier (IMT‑MC)) is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The name cdma2000 actually denotes a family of standards that represent the successive, evolutionary stages of the underlying technology. These are, in order of evolution:

CDMA2000 1xRTT

CDMA2000 1xEV-DO: Release 0, Revision A, Revision B

CDMA2000 1xEV-DO Revision C or Ultra Mobile Broadband (UMB)

CDMA2000 1xEVDV

All are approved radio interfaces for the ITU's IMT-2000. CDMA2000 has a relatively long technical history and is backward-compatible with its previous 2G iteration IS-95 (cdmaOne). In the United States, CDMA2000 is a registered trademark of the Telecommunications Industry Association (TIA-USA).

CDMA2000 1X (IS-2000), also known as 1x and 1xRTT, is the core CDMA2000 wireless air interface standard. The designation "1x", meaning 1 times Radio Transmission Technology, indicates the same radio frequency (RF) bandwidth as IS-95: a duplex pair of 1.25 MHz radio channels. 1xRTT almost doubles the capacity of IS-95 by adding 64 more traffic channels to the forward link, orthogonal to (in quadrature with) the original set of 64. The 1X standard supports packet data speeds of up to 153 kbit/s with real world data transmission averaging 60–100 kbit/s in most commercial applications. IMT-2000 also made changes to the data link layer for greater use of data services, including medium and link access control protocols and QoS. The IS-95 data link layer only provided "best efforts delivery" for data and circuit switched channel for voice (i.e., a voice frame once every 20 ms).