Pier 40 (officially known as Pier 40 at Hudson River Park) is a parking garage, sports facility, and former marine terminal at the west end of Houston Street in Manhattan, New York, within Hudson River Park. It is home to the New York Knights of the USA Rugby League, though it is primarily used by youth and high school athletics.

Pier 40 was originally one of five "finger" piers numbered 37 through 41, which were owned by the government of New York City, and were used by various transport companies. In 1956, the city announced a plan to consolidate the five piers into a single large passenger and cargo terminal serving the Holland America Line. Construction began in 1958 and the terminal was opened in 1962. When the Holland America Line moved to the New York Passenger Ship Terminal in 1974, the pier continued to be used by ships until 1983. Afterward, the New York State Department of Transportation purchased the pier as part of its failed Westway expressway proposal, with plans to use the pier for parking. Pier 40 was redesignated as parkland in 1998; several options for the structure were proposed, including redevelopment as a soccer stadium or an entertainment complex. It reopened in 2005 as a sporting complex within Hudson River Park.

The former cargo terminal is the largest structure in Hudson River Park, with an area of 14.5 acres (5.9 ha), and houses the Hudson River Park Trust's offices. Various park tenants host activities in Pier 40 as well. Sports include baseball, football, soccer, boat building, rowing, flying trapeze, and rugby among others. Despite its popularity, the terminal is dilapidated and sinking into the Hudson River, and was previously proposed for closure due to its deteriorated condition.

Prior to the construction of Pier 40, five city-owned "finger" piers were located at the site. From south to north, these were Pier 37 (at Charlton Street), Pier 38 (at King Street), Pier 39 (at West Houston Street), Pier 40 (at Clarkson Street), and Pier 41 (at Leroy Street). Companies using the piers in the early 20th century included the Southern Pacific Transportation Company, the Delaware, Lackawanna and Western Railroad (DL&W), and the Atlantic Transport Line. By the 1950s, the piers were used by the DL&W and the Baltimore and Ohio Railroad.

The current Pier 40 was proposed as a passenger and cargo terminal in February 1956 by the city's Marine and Aviation Department. The plan was put forward to allow the Holland America Line to move its area operations from Hoboken, New Jersey on the other side of the Hudson River, where the company was based for 73 years. It was the first terminal of its kind to be built by the city, and was designed as a "massive hollow square" with three levels to accommodate cars, taxis, and commercial trucks. The massive four-block structure replaced the five smaller "finger" piers. Construction began on July 31, 1958, at a projected cost of over $18 million. The pier began operations in 1962, with Holland America signing a 20-year lease for over $1.2 million in annual rent. Holland America also moved its offices from the Financial District to Pier 40. In its first year in operation, Pier 40 served over 2,000 passengers daily. In 1971, the Pier was taken over by the Port Authority of New York and New Jersey. Holland America moved their operations to the New York Passenger Ship Terminal in Hell's Kitchen in 1974. Pier 40 ceased serving ships at that time, and ended all operations around 1983.

Following the cessation of maritime operations, in 1982 the Pier was purchased by the State of New York for the failed Westway project. Under the New York State Department of Transportation's operations, its primary use was as a parking complex for cars, buses and trucks, as well as commercial warehousing. Bus, truck, and warehousing activity ended in 2004.

The facility was rededicated under the Hudson River Park act of 1998. At this time, two small athletic fields opened on the pier's roof. Between 1998 and 2003, several plans abound for the redevelopment of the site. One was an entertainment complex featuring movie theaters and Cirque du Soleil performances. Another plan sought to construct a public high school along with swimming pools and retail space, in addition to conventional sports fields. Additional plans called for a branch of the Guggenheim Museum, and a big-box store. Ultimately, a plan backed by the community won out, and the pier currently serves the dual purpose of commercial parking garage (located in the outer perimeter of the pier) and a multi-purpose sports facility (encompassing the center of the facility and small sections of the upper level). The main field, occupying the former cargo level, began construction in 2004, and opened in May 2005 with Governor George Pataki and professional soccer player Eddie Johnson in attendance. The sports fields were intended as an interim solution, until a major development would take place. According to the Hudson River Park Trust, the facility generates $6 million in operating revenue and 40 percent of the entire park's annual operating budget.

Following Hurricane Sandy in 2012, the pier was closed after being engulfed by more than 12 feet (3.7 m) of water. The fields reopened on December 19 following a $50,000 donation to fix the damaged turf surface, while full power was restored by spring 2013.