Romulan Neutral Zone

Facts

Mutually-declared neutral buffer zone between United Federation of Planets and Romulan Star Empire (TOS: "Balance of Terror" et al.)
Formed 2160 following end of Earth-Romulan War by mutual treaty between the two powers
- Modifications to treaty impacting the Neutral Zone made 2311 in the Treaty of Algeron following the Tomed Incident (TNG: "The Pegasus")
All military vessels banned from transit into or through the Neutral Zone
- Exceptions granted on a case-by-case basis upon mutual consent by both governments or their representatives
- Entry without prior authorization grants that nation the right to seize and impound the violating starship (TAS: "The Survivor")
- Treaty of Algeron declared explicitly that unauthorized entry into the Neutral Zone by a military power is to be considered an act of war (TNG: "The Defector")
Civilian unaligned vessels allowed, but closely monitored by both powers
Federation border of Neutral Zone lined with permanent observation asteroid outposts (TOS: "Balance of Terror")
- Gravitic sensor nets were installed along the Federation border to detect entry by cloaked vessels (TNG: "Face of the Enemy")
- This technology was later supplemented with tachyon detection grids (TNG: "Face of the Enemy")
Both nations conduct regular patrols of their border to watch for any undetected incursions (TNG: "Brothers"; Star Trek: First Contact; DS9: "In the Pale Moonlight")