WLIW's multiplex is New York's high-power ATSC 3.0 (NextGen TV) television station and also broadcasts WMBQ-CD.

[3] The Long Island Educational Television Council then applied for and, in June, received a construction permit for channel 21 at Garden City.

[4] Facilities were established on the campus of Nassau Community College, while a 60-hour broadcast week evenly split between in-school instructional and general cultural offerings was slated.

[10] The station finally got studio space when it moved in to the New York Institute of Technology (NYIT) in Westbury in 1974, but that arrangement lasted two years.

[11] As the station investigated studio space at Stony Brook University, it also received federal approval and matching grants to move its transmitter to Plainview and increase power to cover all of Long Island.

In February, the new Plainview transmitter site and studios, at the highest point on Long Island, was activated, significantly improving reception and extending channel 21's reach and capabilities.

[15] John Wicklein assumed the manager post in February 1980 and sought to give the station an identity independent from that of WNET and additional local programming and support.

[29] This spurred the further evolution of WLIW into a regional service as well as a reduced reliance on PBS programs to differentiate the station from WNET.

[34] It also increased its production efforts to the point that 20 percent of its $11 million budget was attributed to selling its output—including ethnic documentaries such as A Laugh, a Tear, a Mitzvah—to other public TV stations.

[35] These were particularly popular for station pledge drives; by the time WLIW and WNET merged in 2003, channel 21 was the leading distributor of such programs, including versions complete with pledge breaks seen nationally, and WLIW manager Terrel Cass attributed the station's continued survival to its foray into national program production.

[37][38] Stimulated by the impending conversion to digital television and necessary equipment expenditures, as well as a grant from the Corporation for Public Broadcasting to explore shared master control functions,[39] WLIW and WNET began engaging in discussions on how to pool primarily technical resources in 2000.

[40] At the initial suggestion of WNET,[41] these conversations soon blossomed into outright merger talks, which lasted months as board members expressed reservations over potential changes and the loss of WLIW's Long Island identity.

The move would save WLIW $5 million in digital conversion costs and reduce duplication of shows between the stations, which would "retain their distinct public identities".

One WLIW board member resigned over what she felt was a reduction of local programming,[44] and longtime Newsday television columnist Marvin Kitman decried an "assault on the public interest" which he compared to appeasement toward Nazi Germany.

In 2015, WNET announced plans to move POV and Independent Lens to WLIW because they failed to hold the viewership of the preceding program, Antiques Roadshow.

[54][55] Nationally distributed public television programming presented by WLIW includes Consuelo Mack WealthTrack, which has been in production since 2005.

[63] A nightly news program was revived in July 1990 with the debut of The 21 Edition; this was canceled the next year due to budget cuts.