It provides crosstown service between western Brooklyn and southwestern Queens and is the only non-shuttle subway line that does not carry trains to and from Manhattan.

[9][10] The first contract to build the Crosstown Line, for a section north of Nassau Avenue in Brooklyn, was awarded in 1928.

[11] The portion of the line crossing Newtown Creek between Brooklyn and Queens, now known as the Greenpoint Tubes, was built without the use of a tunneling shield or compressed air, contrary to the convention of the time.

[12] On August 19, 1933, the line was opened north of Nassau Avenue, and the GG began operation to Queens Plaza.

[15] In 1986, the New York City Transit Authority launched a study to determine whether to close 79 stations on 11 routes, including the entire Crosstown Line, due to low ridership and high repair costs.

[16][17] Numerous figures, including New York City Council member Carol Greitzer, criticized the plans.

[17][18] Over the years, the termini for the GG (relabeled G in 1985)[19] varied, including being extended to Jamaica–179th Street[20] or cut back to Queens Plaza.

On December 16, 2001, a new weekdays-only V train (replaced in 2010 by the M) running local on the Queens Boulevard Line required the truncation of the G to Long Island City–Court Square during weekdays.

In 2012, flood waters from Hurricane Sandy caused significant damage to the Greenpoint Tubes under the Newtown Creek.

[28] On May 16, 2022, the MTA put out the RFP for the design-build contract to install CBTC on the Crosstown Line.

[29] In December 2022, the MTA announced that it would award a $368 million design–build contract to Crosstown Partners, a joint venture between Thales Group and TC Electric LLC.