425 Park Avenue is an office building in New York City redeveloped by L&L Holding and GreenOak Real Estate, with a design by architectural firm Foster + Partners.

The construction of the building began in 1954,[3][4] on land leased from the Robert Walton Goelet estate, who died in 1941.

[6] The 32-story building was open in 1957 with National Biscuit Company,[5] Kaye Scholer, Chemical Corn Exchange Bank as major tenants.

[7][8] Since 2004, L&L Holding, which was founded in 2000, had been trying to redevelop 425 Park Avenue when the Goelet family intended to sell a 33% stake of the property.

After an extended negotiation, L&L, in partnership with Lehman Brothers, entered into a 84-year ground lease deal with the Goelet family in 2006 that was valued at $320 million with a large upfront payment.

However, in 2013, L&L, GreenOak Real Estate, and other investors bought 90% of Lehman Brothers’ stake in the project, allowing L&L to have full control of the redevelopment.

Real estate news site YIMBY noted that, due to its three roughly 200 ft (61 m) concrete fins, the Foster plan would have "[...] the most pronounced skyline effect" compared to the other proposals.

[11] Another key element of Foster + Partners design was the three tiers of very high ceiling and virtually column-free floor space.

[13] The 1961 Zoning Resolution restricted the size of buildings based on floor area ratio (FAR), not height.

The concern was the reason for the city's East Midtown rezoning plan, which added more air rights in the neighborhood immediately around Grand Central Terminal, thereby encouraging redevelopment.

Installing these large temporary steel structures in the middle of a partially demolished building proven to be a challenging and time-consuming process.

[19] The building topped out on December 4, 2018, in a ceremony attended by lead architect Lord Norman Foster.

These concerns were officially allayed in January 2019 when Citadel executed a lease expansion for another 124,000 sq ft (11,500 m2) of space, bringing their total occupancy to 16 floors of the building.