Under the terms of the New Vegas treaty, the New California Republic (NCR) was able to establish an embassy on the Strip to resolve and negotiate issues with Mr. House. It is located at the end of the strip, within a rundown building (which is due to Mr. House's dislike of the NCR). The embassy has had 3 Ambassadors since its creation:
The NCR Embassy compound consists of two buildings: the embassy itself; and the NCR Military Police Headquarters. During the day, Crocker can be found in his office within the embassy, one of few rooms to the left of the reception desk (or as the receptionist will inform you, at her right). On your left (her right) there are several supply rooms, a barracks room, a dining hall, and Marie Pappas' office.
Upon a second visit to the embassy the player may be approached by an MP. If you have Lily or Raul as a companion he will initiate speech and comment about them being allowed onto the strip and end the dialog there. If any "normal" human companions are in tow he will initiate an idle conversation, e.g. "What do you need?", with the player's answer ending the conversation.
If you visit this embassy after receiving the quest Don't Tread on the Bear!, you may be confronted by an NCR MP who expresses his displeasure with you being on the strip. He and every MP within the embassy becomes hostile, including Captain Marie Pappas. You will gain NCR Infamy even if you don't defend yourself. The only people left alive are Liza O'Malley, the Ambassador, and Jake Erwin. Even upon exiting the embassy, the remaining patrolling NCR MP's are hostile to you.
During the final battle at Hoover Dam, it can be heard on the NCR emergency radio broadcast that the embassy is being bombed by the Omertas, if they weren't taken care of beforehand.
The windows inside the NCR Embassy are both different from the outside windows, and unique throughout the game.