Pacific Park is a mixed-use commercial and residential development project by Forest City Ratner in Brooklyn, New York City. It will consist of 17 high-rise buildings near Brooklyn's Prospect Heights, adjacent to Downtown Brooklyn, Park Slope, and Fort Greene neighborhoods. The project overlaps part of the Atlantic Terminal Urban Renewal Area, but also extends toward the adjacent brownstone neighborhoods. Of the 22-acre (8.9 ha) project, 8.4 acres (3.4 ha) is located over a Long Island Rail Road train yard. A major component of the project is the Barclays Center sports arena, which opened on September 21, 2012. Formerly named Atlantic Yards, the project was renamed by the developer in August 2014 as part of a rebranding.

The development of Pacific Park is overseen by the Empire State Development Corporation. As of 2018^[update], four of fifteen planned buildings had opened, but the deadline was delayed by about 10 years from 2025 to 2035. The residential component includes the world's tallest modular apartment building, 461 Dean, opened in November 2016.

Since the mid-20th century, there have been many proposals to develop the area around Flatbush and Atlantic Avenues, known as Times Plaza; however, plans for the area emerged only piecemeal. In the mid-1950s, Brooklyn Dodgers owner Walter O'Malley proposed that the city condemn the site, where he could then have built a new stadium for the ball club to replace Ebbets Field. City officials refused to condemn the property for subsequent sale to O'Malley on the grounds that they did not consider a privately financed baseball park to be an appropriate public purpose as defined under Title I of the Federal housing act of 1949. O'Malley's proposal was dismissed by Robert Moses for creating a Great Wall of traffic. In 1958, O'Malley relocated the Dodgers to Los Angeles. In 1968, Long Island University eyed the site, but was opposed by Mayor John V. Lindsay.

A 1968 New York Times article described a $250 million (over $1.4 billion in March 2006 dollars) plan for the Atlantic Terminal Urban Renewal Area, also known as ATURA. According to the Times, the renewal plan "calls for 2,400 new low- and middle-income housing units to replace 800 dilapidated units, removal of the blighting Fort Greene Meat Market, a 14-acre (6 ha) site for the City University's new Baruch College, two new parks, and community facilities such as day-care centers."

The 1970s also saw plans for ambitious projects in the area, and these mostly resulted in the construction of affordable housing on the north side of Atlantic Avenue. Baruch College also considered moving but was stymied by the city's fiscal crisis.

In the 1980s, a Fort Greene block association and other homeowners sued over an environmental impact statement that failed to consider how rerouted traffic would affect their neighborhood, one block away from the project. Then an economic downturn compounded community opposition. The Times reported that the stock market collapse had deterred office construction. "A lot of people are reassessing their expansion plans," James Stuckey, president of the city's Public Development Corporation, told the Times in 1988.

Plans for Atlantic Yards were announced on December 10, 2003. Its name, devised by developer Forest City Ratner, relates to the rail yard located between Atlantic Avenue and Pacific Street. At the time, the development was to include 2,250 residences and some commercial space on Pacific Street from Vanderbilt to Fourth avenues. There were also plans for a 20,000-seat arena for the New Jersey Nets. Officially, the Long Island Rail Road yard is called the "Vanderbilt Yard" by the Metropolitan Transportation Authority (MTA), named for Vanderbilt Avenue, which crosses over on its way to the Brooklyn Navy Yard. The LIRR's nearby Atlantic Terminal station is the westernmost stop of the Atlantic Branch. Easy access by rapid transit and suburban rail, and the desirable brownstone housing stock nearby made it a target for speculative development.

The Pacific Park project was originally developed and overseen by Forest City Ratner, an arm of Forest City Enterprises, of Cleveland, Ohio. The original master plan and some individual buildings were developed by architect Frank Gehry. Gehry was removed from the project in June 2009. After September 2009, the design for what became Barclays Center became a collaboration between Ellerbe Becket and the Manhattan architectural firm SHoP Architects. Pacific Park, overseen by the Empire State Development Corporation (ESDC), is supposed to be a public-private project, Bruce Ratner told Crain's New York Business in November 2009.