The High Line is a 1.45-mile-long (2.33 km) elevated linear park, greenway, and rail trail created on a former New York Central Railroad spur on the West Side of Manhattan in New York City. The High Line's design is a collaboration between James Corner Field Operations, Diller Scofidio + Renfro, and Piet Oudolf. The abandoned spur has been redesigned as a "living system" drawing from multiple disciplines which include landscape architecture, urban design, and ecology. The High Line was inspired by the 4.7 km (2.9 mi) long Coulée verte (tree-lined walkway), another elevated park in Paris completed in 1993.

The park is built on an abandoned, southern viaduct section of the New York Central Railroad's West Side Line. Originating in the Meatpacking District, the park runs from Gansevoort Street—three blocks below 14th Street—through Chelsea to the northern edge of the West Side Yard on 34th Street near the Javits Center. The West Side Line formerly extended south to a railroad terminal at Spring Street, just north of Canal Street, and north to 35th Street at the site of the Javits Center. Due to a decline in rail traffic along the rest of the viaduct, it was effectively abandoned in 1980 when the construction of the Javits Center required the demolition of the viaduct's northernmost portion. The southern portion of the viaduct was demolished in segments during the late 20th century.

A nonprofit organization called Friends of the High Line was formed in 1999 by Joshua David and Robert Hammond, advocating its preservation and reuse as public open space, an elevated park or greenway. Celebrity New Yorkers joined in on fundraising and support for the concept. The administration of Mayor Michael Bloomberg announced plans for a High Line park in 2003. Repurposing the railway into an urban park began in 2006 and opened in phases during 2009, 2011, and 2014. The Spur, an extension of the High Line that originally connected with the Morgan General Mail Facility at Tenth Avenue and 30th Street, opened in 2019. The Moynihan Connector, extending east from the Spur to Moynihan Train Hall, opened in 2023.

Since opening in June 2009, the High Line has become an icon of American contemporary landscape architecture. The High Line's success has inspired cities throughout the United States to redevelop obsolete infrastructure as public space. The park became a tourist attraction and spurred real estate development in adjacent neighborhoods, increasing real-estate values and prices along the route. By September 2014, the park had nearly five million visitors annually, and by 2019, it had eight million visitors per year.

The High Line extends for 1.45 miles (2.33 km) from Gansevoort Street to 34th Street. At 30th Street the elevated tracks turn west around the Hudson Yards Redevelopment Project to the Jacob K. Javits Convention Center on 34th Street. As proposed, the park was to be integrated with the Hudson Yards development and the Hudson Park and Boulevard. If Hudson Yards' Western Rail Yard is built, it will be elevated above the High Line Park, so an exit along the viaduct over the West Side Yard will lead to the Western Rail Yard. The 34th Street entrance is at grade, with wheelchair access.

The park is open daily from 7:00 a.m. to 10:00 p.m. through the warmer months, and until 8:00 p.m. in winter. It can be reached through eleven entrances, five of which are accessible to people with disabilities. The wheelchair-accessible entrances, each with stairs and an elevator, are at Gansevoort, 14th, 16th, 23rd, and 30th Streets. Additional staircase-only entrances are located at 18th, 20th, 26th, and 28th Streets, and 11th Avenue. Street-level access is available at 34th Street via the Interim Walkway, which runs from 30th Street and 11th Avenue to 34th Street west of 11th Avenue.

At the Gansevoort Street end (which runs north–south), the stub over Gansevoort Street is named the Tiffany and Co. Foundation Overlook and was dedicated in July 2012; the foundation was a major supporter of the park. The southern terminus of the park also contains a small wooded area called the Gansevoort Woodland. The route then passes under The Standard, High Line hotel and through a passage at 14th Street. At 14th Street, the High Line splits into two sides at different elevations; the Diller-Von Furstenberg Water Feature (opened in 2010) is on the lower side, and a sundeck is on the upper side.

The route passes through the west edge of the Chelsea Market, a food hall, at 15th Street. A spur, connecting the viaduct to the National Biscuit Company building and closed to the public, splits off at 16th Street. The railroad tracks on the spur are left in situ but the trackbeds are planted with greenery. The Tenth Avenue Square, an amphitheater on the viaduct, is at 17th Street where the High Line crosses over Tenth Avenue from southeast to northwest. At the 23rd Street Lawn, visitors can rest. Between 25th and 26th Streets a ramp takes visitors above the viaduct, with a scenic overlook facing east at 26th Street. The Philip Falcone and Lisa Maria Falcone Flyover, named after two major donors to the park, was based on plans for a Phase 1 flyover which was never built.