The Treaty of Algeron is an agreement referred to in Star Trek: The Next Generation between the United Federation of Planets and the Romulan Star Empire. Only mentioned twice in the series (in the TNG episodes "The Defector" and "Pegasus"), this treaty ratified in 2311 reaffirmed the boundaries of the Neutral Zone and prohibited the Federation from developing a cloaking device or cloaking technology.

Further details on the circumstances leading to the Treaty of Algeron are given in David R. George III 's 2003 Star Trek novel Serpents Among the Ruins.