The Third and Lexington Avenues Line, also known as the Third Avenue Line, is a public transit line in Manhattan, New York City, running from Lower Manhattan to Fort George in Washington Heights. Originally a streetcar line, it now consists of the M98, M101, M102, and M103 bus routes, operated by the New York City Transit Authority. The M98 bus route operates on Third Avenue between East 65th Street and East 127th Street, although it previously continued to 32nd Street. The M101, M102 and M103 bus routes run southbound on Lexington Avenue north of East 24th Street.
 The M98 operates between Hunter College at East 68th Street on the Upper East Side and Fort Tryon Park in Inwood near West 192nd Street. The M98 operates northbound via Third Avenue, and southbound via Lexington Avenue. At East 120th Street, southbound service shifts from Park to Lexington Avenues, while at East 127th Street, the M98 northbound service shifts onto the Harlem River Drive. The M98 exits the Harlem River Drive via the Interstate 95/Amsterdam Avenue exit. The M98 travels westbound along West 179th Street and eastbound along West 178th Street between Amsterdam Avenue and Fort Washington Avenue, where the M98 turns north on Fort Washington Avenue until its terminal at the entrance to Fort Tryon Park.
 The M101 spans between Cooper Square in the East Village and West 193rd Street and Amsterdam Avenue in Fort George. The M101 runs northbound along Third Avenue from Astor Place to East 125th Street, while southbound buses use Lexington Avenue north of East 24th Street. The M101 continues crosstown on 125th Street to Amsterdam Avenue, running north towards West 193rd Street after Amsterdam Avenue becomes Fort George Avenue. To begin the southbound trip, the M101 turns south onto Saint Nicholas Avenue, then left (east) onto West 190th Street, followed by a right (south) back onto Amsterdam Avenue.
 The M101 runs as a limited-stop service during the day south of East 116th Street, with no other local service. Local service is provided by the M102 and M103 buses, during that time. Overnight and weekend morning service runs local.
 The M102 begins at Cooper Square and follows the M101 until East 116th Street in East Harlem. The route travels west across 116th Street to Lenox Avenue, where it continues north to the Harlem–148th Street subway station.
 The M103 begins its route at City Hall and travels north via Park Row and the Bowery. At Astor Place, it continues north alongside the M101 and M102 along Third to East 125th Street, where it terminates. Southbound service uses Lexington Avenue from East 125th to 24th Streets, then uses Third Avenue, Bowery, and Park Row.
 The Third Avenue Railroad opened a line in 1853, from Astor House at Broadway and Park Row to 86th Street, running north along Park Row, Bowery, where it shared tracks with the Second Avenue Line, and Third Avenue. In 1859, an extension to East Harlem opened. Using the 125th Street Crosstown Line and tracks along Amsterdam Avenue, Third Avenue cars were also operated to Fort George. A trolley park called the Fort George Amusement Park operated at that end of the line from 1895 to 1914.
 New York Railways' Lexington Avenue Line streetcar was replaced by New York City Omnibus Corporation (NYCO) bus (M21 - 3/4) on March 25, 1936. In 1936, the NYCO and Fifth Avenue were placed under common ownership. In 1941, Surface Transportation Corporation began operating former Third Avenue Railway routes. The Third Avenue Railway's Third Avenue and Amsterdam Avenue Line streetcar was replaced by the M101 bus operated by the Surface Transportation Corporation on May 18, 1947.
 On July 17, 1960, Third Avenue north of 24th Street became one-way northbound, and southbound buses were moved to Lexington Avenue, and the two parallel bus lines were combined as a one-way pair, keeping the route number M101.
 After a strike in 1962, the entire Fifth Avenue system was transferred to the newly formed Manhattan and Bronx Surface Transit Operating Authority on March 22, 1962.
 Route M101A, formerly NYCO Fifth, Madison and Lenox Avenues route 2, was started on March 2, 1969. This route was renumbered the M102 on July 1, 1974.
 New M98 Limited Stop service running between 32nd Street and Washington Heights was introduced on September 14, 1987, as a rush hour-only service. A public hearing had been held on March 12, 1987 concerning the proposed introduction of the route. Service initially ran every 15 minutes between 6:30 and 9:30 a.m. southbound, and every 15 minutes northbound from 4 to 7 p.m.. with service every 30 minutes in the reverse-peak. Stops were added to the route in response to community requests at 187th Street, 125th Street, 116th Street and 107th Street. The route was designed to keep the number of stops to a minimum to attract ridership.
 Limited-stop service on the M101 began on October 14, 1991, with alternate buses running limited between 7 a.m. and 7 p.m.
 On September 10, 1995, the M103 was created to improve reliability along Third and Lexington Avenues, curtailing the M101 and M102 south of Astor Place.
 In 2009, buses along the corridor were involved in a total of 268 accidents. The number is attributed to both inexperienced operators and the number of "obstacles" along the route.
 On June 27, 2010, due to shortfalls in the Metropolitan Transportation Authority's budget, the M98 was truncated from 32nd Street to 68th Street. At the same time, southbound M98 service into the George Washington Bus Terminal was discontinued. These two changes were estimated to annually save $800,000.