Eircom Limited, trading as Eir (/ɛər/ AIR; stylised eir), is a large fixed, mobile and broadband telecommunications company in Ireland. The company, which is currently incorporated in Jersey, traces its origins to Ireland's former state-owned monopoly telecommunication provider Telecom Éireann and its predecessors, P&T (the Dept. of Posts and Telegraphs) and before the foundation of the state, the telecommunications division of the GPO. It remains the largest telecommunications operator in Ireland and has overseas operations focused on the business and corporate telecom markets in the United Kingdom. The company was in majority state ownership until 1999, when it was privatised through a flotation on the Irish and New York Stock Exchanges.

Eir is currently majority owned by Xavier Niel's Iliad SA and his Paris-based NJJ Telecom Europe investment fund (64.5%). The group includes French telecommunications provider Free and Iliad Italia. Other major investors include Anchorage Capital Group (26.6%), and Davidson Kempner (8.9%).

Eir operates a wholesale fixed-line network through its Open Eir unit, providing copper and fibre based access products to a wide range of Irish telecommunications companies. Its services include next generation access products, such as FTTH, FTTC (VDSL) and legacy copper based services, including ADSL and classic digital circuit switched products like PSTN and ISDN. It also offers a range of legacy leased line services.

The company's retail division markets these services directly to homes and businesses, and includes value added services like Eir TV and voice over broadband for home users and a wide range of digital services tailored to business customers.

Eir operates a national mobile network both under its own Eir brand and GoMo, a value-focused, online-only sub-brand. The network provides 2G, 3G, 4G and 5G services and ancillary services such as WiFi Calling and VoLTE.

In the third quarter of 2019, Eir accounted for 39% of the Ireland's fixed voice market retail revenue and 45.3% market share by fixed-line retail and wholesale revenue and 19.1% of the mobile market (excluding mobile broadband and machine-to-machine subscriptions) or 15.6% of total subscriptions. Eir had 31.4% of fixed broadband subscriptions (comprising FTTH, FTTC/VDSL and ADSL) and 42.7% of FTTP subscriptions.

Its main fixed access infrastructure owning competitors are Virgin Media Ireland (which operates a cable TV and broadband network) and SIRO, a joint venture between publicly owned energy supplier, ESB and Vodafone. SIRO operates a FTTH network using ESB's physical infrastructure to carry fibres to individual homes and businesses. Imagine Communications, Digiweb and several other smaller ISPs also operate their own wireless networks using various technologies. Eir also faces retail competition from Vodafone, Sky, Digiweb and a large number of smaller ISPs using a mix wholesale access from Open Eir and SIRO to reach their customers.

Eir also faces competition from mobile operators and MVNOs both for its own mobile services and also as fixed line replacement products. All mobile operators are capable of offering very competitive voice services and high speed 4G and increasingly 5G connectivity, which can often be faster than fixed services, particularly first generation NGA products using VDSL and fibre to cabinet, which can only offer a maximum of 100 Mbit/s. ADSL services which are much slower again. 4G and 5G fixed-mobile services, using routers and external antennae have also become viable competitors in many rural and quasi rural areas. These offer ample and affordable data plans and very high speeds and a number of operators have designed products targeting homes and businesses using both existing mobile and dedicated LTE and 5G networks.