Prior to the dissolution of the Soviet Union in 1991, the Caspian was claimed by only Iran and the Soviet Union, who understood the legal regime for this maritime space to be that of a lake. Following the breakup of the Soviet Union, four former States of the Soviet Union joined Iran as countries encircling the Caspian Sea, those being Azerbaijan, Kazakhstan, Russia and Turkmenistan. These newly established littoral States had differing views as to whether the Caspian was to be considered a ‘lake’ or a ‘sea,’ and, more importantly, what principles of maritime law should be applied to delimit this enclosed body of water.

Kazakhstan and Russia defined their maritime boundary through an agreement reached in 1998, before the overall question on the status of the Caspian Sea had been resolved. The two States utilized a modified equidistance boundary to delimit their overlapping claims. The boundary line extends in a southerly direction for 320 nautical miles, from their land boundary terminus to a defined tripoint with Azerbaijan.

In 2018, the littoral States encircling the Caspian signed a convention in which they agreed to a special legal status for these waters. Under the provisions of the Convention, each bordering State could claim a fifteen nautical mile territorial sea and a ten nautical mile fishery zone. The remaining waters of the Caspian would be left open to free navigation by all five Parties, while the rights to the seabed would be defined by agreement between them.

Kazakhstan and Russia have made no additional agreements regarding their maritime boundary since the signature of the Caspian Sea Convention in 2018, but its initial delimitation is generally in conformity with the provisions of that document.

Kazakhstan and Russia also share a land boundary.