Category 5 cable (CAT-5) is a computer network Ethernet cable standard as defined by the Electronic Industries and Telecommunications Industry Association (EIA/TIA). This 5th generation twisted pair Ethernet cabling system contains copper wire in four pairs. It has recently been replaced by the Category 5E (CAT-5E) specification.

CAT-5 structured cabling was designed for high signal integrity. It can carry many signals such as basic voice services among others. Local Area Network (LAN)–based computers mostly use CAT-5 cable connections. Networks that can use CAT-5 are ATM, token ring, 10Base-T, 100Base-T, and 1000Base-T.

CAT-5 cabling has four twisted pairs of wires in one cable jacket. These wires terminate in RJ45 connectors and preserve a high signal-to-noise ratio in spite of interference (crosstalk) from other pairs and external sources. This network cabling system can maintain frequencies of up to 100 MHz and speeds of up to 1000 Mbps. Typical CAT-5 cables have three twists per inch in each twisted pair of 24-gauge copper wire.

CAT-5 cable is produced in two forms: stranded form and solid form.

The stranded form is more flexible and less susceptible to breakage. This form is suitable for reliable connections with insulation-piercing connectors, but not for connectors of the insulation-displacement type.

The solid form is less expensive. It is suited to creating reliable connections with insulation-displacement connectors, but not for connectors of the insulation-piercing type.

Considering these characteristics, building wiring (wall socket to central patch panel) should be solid, while patch cable (movable cable that plugs into the wall socket and a computer) should be stranded core.

Category 5E (CAT-5E) is a newer version of CAT-5 which adds specifications for far-end crosstalk. Formally classified in 2001 as the TIA/EIA-568-B standard, it no longer uses the traditional CAT-5 specifications. The 1000Base-T networks were designed to use CAT-5 cables, but the enhanced specifications attributed to the CAT-5E cables and connectors make it a better choice for use within 100Base-T. The CAT-5E cable system does not allow longer cable distances within the Ethernet networks, despite the improvement in performance specifications. Its cable length is limited to 100 meters (328 feet) maximum.