Prince Saionji Kinmochi (Japanese: 西園寺 公望; 7 December 1849 – 24 November 1940) was a Japanese statesman and diplomat who twice served as Prime Minister of Japan, in 1906–1908 and 1911–1912. He was the last surviving member of the genrō, the small group of unofficial elder statesmen who dominated Japanese politics during the Meiji and Taishō periods. As a member of the Kyoto court nobility (kuge), Saionji forged a close relationship with the imperial house from a young age and participated in the Boshin War that overthrew the Tokugawa shogunate. He spent nearly a decade studying in France, where he became a heartfelt Francophile deeply influenced by European liberalism.
Upon his return to Japan, Saionji held a series of high-ranking posts in the Meiji government, including diplomat and cabinet minister, often under the patronage of Itō Hirobumi. In 1903, he succeeded Itō as president of the Rikken Seiyūkai political party and entered into a political compromise with his rival, General Katsura Tarō. For the next decade, a period known as the Keien era, the two men alternated as prime minister, with Saionji leading cabinets from 1906 to 1908 and again from 1911 to 1912.
Following the Taishō political crisis of 1912–1913, Saionji was elevated to the rank of genrō. For the next quarter-century, he played a crucial role in Japanese politics, primarily through his power to recommend prime ministerial candidates to the Emperor. As the most liberal of the elders, he championed party-based governments during the 1920s, a period known as "Taishō democracy". He also led the Japanese delegation at the Paris Peace Conference in 1919, where he took a background role while securing territorial gains for Japan. As the sole surviving genrō from 1924, his power to restrain the growing influence of the military proved limited. With the rise of militarism in the 1930s, Saionji's influence waned, and he witnessed the collapse of the liberal, pro-Western political order he had spent his life building. He retired from politics in 1937 and died in 1940, a year before Japan's entry into the Second World War.