Which of these countries lies both in Asia and Europe?

The conventional Europe-Asia boundary was subject to considerable variation during the 18th and 19th centuries, indicated anywhere between the Don River and the Caucasus to the south or the Ural Mountains to the east. Since the later 19th century, the Caucasus-Urals boundary has become almost universally accepted. According to this now-standard convention, the boundary follows the Aegean Sea, the Turkish Straits, the Black Sea, along the watershed of the Greater Caucasus, the northwestern portion of the Caspian Sea and along the Ural River and Ural Mountains to the Arctic Ocean.

According to this convention, the Russian Federation, the Republic of Turkey, Kazakhstan, Azerbaijan and Georgia have territory both in Europe and in Asia.

The territory of the Republic of Turkey is predominantly in Asia, with European Turkey (East Thrace) accounting for about 11 million people, or some 14% of the country's population.The Turkish city Istanbul (ancient Constantinople) lies on both sides of the Bosporus, making it a "transcontinental city". Çanakkale is also a Turkish city situated on two continents.