Park 51 is the current name for a proposed Islamic community center and mosque near the World Trade Center site, although not in line of sight of it. Formerly named Cordoba House, it is called the 9-11 Mosque or Ground Zero Mosque by opponents, and is highly controversial. Many of the opponents believe it is disrespectful to the victims of the 9-11 Attack in New York, since radical Islamists belonging to al-Qaeda carried out the attack, to have any Muslim-affiliated sites within the general area of the attacks. While now cleared, some debris and human remains fell in the area of the proposed construction.
Other non-Muslim proponents argue that it is a symbol of religious freedom and freedom of speech, values very much not part of radical Islam. Both sides claim to be fighting radical Islam. Public opinion is generally against it, with a CNN–Opinion Research Corporation poll showing opposition from 70% of Americans polled. 
The new name is derived from the address, 51 Park Place.
Cordoba House was controversial because some believed it was a reminder of Muslim conquests of Cordoba, Spain.
Leading the program are Imam Faisal Abdul Rauf and his wife Daisy Khan. Rauf founded the American Society for Muslim Advancement. Rauf has been associated with Hamas, and has, when asked about terrorism, "“The issue of terrorism is a very complex question....I wouldn’t say that the United States deserved what happened, but the United States policies were an accessory to the crime that happened.”
- Senate Majority Whip Dick Durbin (D-IL)
- Sen. Jeff Merkley (D-OR)
- Sen. Russ Feingold (D-WI)
- Sen. Patrick Leahy (D-VT)
- Sen. Al Franken (D-MN)
- Rep. Keith Ellison (D-MN)
- Rep. Shelly Berkley (D-NV)
- Rep. Jerrold Nadler (D-NY)
- Rep. Carolyn Maloney (D-NY)
- Rep. Ron Paul(R-TX)
- Rep. Andre Carson (D-IN)
- Rep. Kathy Dahlkemper (D-PA)
- Governor Charlie Crist (I-FL)
- Mayor Michael Bloomberg, who said on 3 August, "we would play into our enemies' hands" if we were to deny American Muslims the right to build a mosque where they choose..To cave to popular sentiment would be to hand a victory to the terrorists."
- Keith Olbermann of MSNBC
Opposition splits on no specific lines. While National Review editorially endorsed a boycott of contractors, one of its columnists called such action unwise.  Josh Barrow argued that several proposed restrictions are specific to Islam, and are unwise precedents in the particular geography of Lower Manhattan.
- Samuel Goldsmith (14 July 2010), "Cordoba House mosque near Ground Zero slaps new name on itself with Park51", New York Daily News
- Romesh Ratnesar (18 August 2010), "Ground Zero: Exaggerating the Jihadist Threat", Time
- Editors of National Review (4 August 2010), "Not at Ground Zero", National Review Online
- Action Alert: Call and Thank the Voices of Tolerance and Unity Now!, American-Arab Anti-Discrimination Committee, 30 August 2010
- Josh Barro (15 August 2010), "A Very Long Post on Cordoba House", National Review Online