Western Armenia (Western Armenian: Արեւմտեան Հայաստան, Arevmdian Hayasdan) is a term to refer to the eastern parts of Turkey (formerly the Ottoman Empire) that are part of the historical homeland of the Armenians. Western Armenia, also referred to as Byzantine Armenia, emerged following the division of Greater Armenia between the Byzantine Empire (Western Armenia) and Sassanid Persia (Eastern Armenia) in 387 AD.

The area was conquered by the Ottomans in the 16th century during the Ottoman–Safavid War (1532–1555) against their Iranian Safavid arch-rivals. Being passed on from the former to the latter, Ottoman rule over the region became only decisive after the Ottoman–Safavid War of 1623–1639. The area then became known also as Turkish Armenia or Ottoman Armenia. During the 19th century, the Russian Empire conquered all of Eastern Armenia from Iran, and also some parts of Turkish Armenia, such as Kars. The region's Armenian population was affected during the widespread massacres of Armenians in the 1890s.

The Armenians living in their ancestral lands were exterminated or deported by Ottoman forces during the 1915 Armenian genocide and over the following years. The systematic destruction of Armenian cultural heritage, which had endured over 4000 years, is considered an example of cultural genocide. Assimilated and crypto-Armenians still live in the area today, and some irredentist Armenians living both in Turkey and in exile it as part of United Armenia or as a Sovereign state. The most notable political party with these views is the Armenian Revolutionary Federation.

Since 2000, an organizing committee of the congress of heirs of Western Armenians who survived the Armenian genocide is active in diasporan communities. On August 10, 2020, the three traditional Armenian parties—the Armenian Revolutionary Federation (ARF, Dashnaks), Social Democrat Hunchakian Party (Hunchaks) and the Armenian Democratic Liberal Party (Ramgavars)—issued a joint statement on the centenary of the Sèvres Treaty, stating that the treaty is the only international document defining the border between Armenia and Turkey. "The Treaty of Sevres is a valid international treaty, although it has not been ratified by all signatories, but it has not been legally replaced by any other international instrument. At least from the point of view of the rights of the Armenian Cause, the Republic of Armenia and the Armenian nation, it remains a promissory note based on international law."

A 2014 survey in Armenia asked what kind of demands should Armenia make to Turkey. Some 80% agreed that Armenia should make territorial claims (30% said only territorial claims, while another 50% said territorial, moral, financial, and proprietary). Only 5.5% said no demands should be made. According to a 2012 survey, 36% of Armenians asked agree or somewhat agree that Turkish recognition of the Armenian Genocide will result in territorial compensation, while 45% believe it will not. The online publication Barometer.am wrote: "It appears that our pragmatic population believes that all possible demands should be forwarded to Turkey [...] but a relative majority consider the practical realization of territorial claims to Turkey is unrealistic."