Lawful interception (LI) refers to the facilities in telecommunications and telephone networks that allow law enforcement agencies with court orders or other legal authorization to selectively wiretap individual subscribers. Most countries require licensed telecommunications operators to provide their networks with Legal Interception gateways and nodes for the interception of communications. The interfaces of these gateways have been standardized by telecommunication standardization organizations. As with many law enforcement tools, LI systems may be subverted for illicit purposes.
With the legacy public switched telephone network (PSTN), wireless, and cable systems, lawful interception (LI) was generally performed by accessing the mechanical or digital switches supporting the targets' calls. The introduction of packet switched networks, softswitch technology, and server-based applications during the past two decades fundamentally altered how LI is undertaken.
Lawful interception differs from the dragnet-type mass surveillance sometimes done by intelligence agencies, where all data passing a fiber-optic splice or other collection point is extracted for storage or filtering. It is also separate from the data retention of metadata that has become a legal requirement in some jurisdictions.