The Ryukyu Islands (琉球諸島, Ryūkyū-shotō), also known as the Nansei Islands (南西諸島, Nansei-shotō, lit. "Southwest Islands") or the Ryukyu Arc (琉球弧, Ryūkyū-ko), are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonaguni the westernmost. The larger are mostly high islands and the smaller mostly coral. The largest is Okinawa Island.

The climate of the islands ranges from humid subtropical climate (Köppen climate classification Cfa) in the north to tropical rainforest climate (Köppen climate classification Af) in the south. Precipitation is very high and is affected by the rainy season and typhoons. Except the outlying Daitō Islands, the island chain has two major geologic boundaries, the Tokara Strait (between the Tokara and Amami Islands) and the Kerama Gap (between the Okinawa and Miyako Islands). The islands beyond the Tokara Strait are characterized by their coral reefs.

The Ōsumi and Tokara Islands, the northernmost of the islands, fall under the cultural sphere of the Kyushu region of Japan; local inhabitants speak a variation of the Kagoshima dialect of Japanese. The Amami, Okinawa, Miyako, and Yaeyama Islands have a native population collectively called the Ryukyuan people, named for the former Ryukyu Kingdom that ruled them. The varied Ryukyuan languages are traditionally spoken on these islands, and the major islands have their own distinct languages. In modern times, the Japanese language is the primary language of the islands, with the Okinawan Japanese dialect prevalently spoken. The outlying Daitō Islands were uninhabited until the Meiji period, when their development was started mainly by people from the Izu Islands south of Tokyo, with the people there speaking the Hachijō language.

The islands were held by the United States after the 1951 Treaty of San Francisco concluded the Pacific War. They were returned to Japan under the 1971 Okinawa reversion agreement, with China disputing the Senkaku Islands.

Administratively, the islands are divided between two prefectures: the northern islands, collectively called the Satsunan Islands, are part of Kagoshima Prefecture (specifically Kagoshima District, Kumage Subprefecture/District, and Ōshima Subprefecture/District), while the southern part of the chain makes up Okinawa Prefecture. The divide is between the Amami and Okinawa Islands, with the Daitō Islands part of Okinawa Prefecture.