The Treaty of Algeron, in the Star Trek Universe, was a compact agreed upon by the Representatives of the United Federation of Planets and the Romulan and Klingon Empires. It re-affirmed establishment of Neutral Zone Borders between the three powers as they existed before the Tomed Incident of 2311, and called for the Federation to renounce all research into the development of cloaking technology for it's Star Fleet starships.

Historical side note: Not all members of Star Fleet felt obliged to abide by the terms of this treaty. Captain (Later Admiral) Eric Pressman and a number of other individuals conspired together in the 2350's to develope, implement, and test a type of cloaking technology for installation on Star Fleet vessels which also had the added benefit of allowing the cloaked vessel to "phase" itself slightly out of line with our universe and then pass through solid objects, such as Asteroids.