IP多媒体子系统（IP Multimedia Subsystem，IMS）是一个基于IP网提供话音及多媒体业务的网络体系架构。它最初是由无线标准化组织 3GPP设计的，作为其GSM之后的未来移动网络远景目标的一部分。

IMS的最初的版本（3GPP R5）主要是给出了一种基于GPRS来实现IP多媒体业务的方法。在这个版本的基础上，3GPP, 3GPP2 以及 TISPAN进行了进一步的更新，以支持GPRS之外的，诸如 WLAN, CDMA2000 和固定等其他接入网络。从目前来看，IMS是独立于接入网技术的，虽然IMS与底层传输功能有着很多联系。

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is an architectural framework for delivering IP multimedia services. Historically, mobile phones have provided voice call services over a switched-circuit-style network, rather than strictly over an IP packet-switched network. Alternative methods of delivering voice or other multimedia services over IP have become available on smartphones (e.g. VoIP or Skype), but they have not become standardized across the industry. IMS is an architectural framework to provide such standardization.