The Federation-Cardassian Treaty was a treaty signed between the United Federation of Planets and the Cardassian Union in 2370. Three years earlier, in 2367, the Federation-Cardassian Armistice of 2367 had been signed between the Federation and Cardassia to end major engagements; this treaty was supposed to be the final end to the hostilities of the Federation-Cardassian War and the Federation-Cardassian Armistice of 2367. (TNG: "Journey's End", "Preemptive Strike")
The Treaty was primarily negotiated by Admiral Alynna Nechayev, and mainly dealt with the status of the Federation-Cardassian border, leading to the establishment of the Demilitarized Zone. Within the Zone, neither side was permitted to deploy armaments, or establish military bases. The official border, which ran through the zone, was redrawn requiring the exchange of several worlds. Although the colonists on these worlds were given the option of resettlement, many refused as they felt that their rights had been ignored. The resulting dissatisfaction eventually led to the establishment of the underground insurgency group called Maquis. (DS9: "The Maquis, Part I", "The Maquis, Part II"; VOY: "Prime Factors", "Tattoo", "Investigations")
The Dominion was aware of the treaty being signed and Talak'talan mentioned it to Benjamin Sisko in late 2370. The Jem'Hadar considered it to be "a tactical error" on the Federation's part. (DS9: "The Jem'Hadar")
In his message to the Cardassian government in 2371, Enabran Tain mentioned this treaty and the Bajoran-Cardassian Treaty as the factors which blinded it to the danger of the Dominion. (DS9: "The Die is Cast")
After the annexation of the Cardassian Union by the Dominion the treaty was effectively void. Any further negotiations between the Federation and the Cardassians would have been carried out as part of the Dominion War peace treaty.