The Taiwan Strait or Formosa Strait, formerly known as the Black Ditch, is a 180-km-wide (111.85-mile-wide) strait separating the island of Taiwan from the Asian mainland. The strait is part of the South China Sea and connects to East China Sea to the northeast. The narrowest part is 130 km (81 mi) wide.

Fujian province in mainland China is to the west of the strait, while important islands like Quemoy, Xiamen Island, Pingtan Island, and the Matsu Islands lie just off the coast. To the east are the west coasts of Taiwan and Penghu. The island fishermen use the strait as a fishing resource. The Min and Jiulong Rivers empty into the strait.

There have been discussions about the strategic importance of the Taiwan Strait. Some Japanese politicians claimed that the Taiwan Strait is an essential sea route for oil shipment from the Middle East via the Malacca Strait to Japan. However, some have argued that this is merely an excuse for intervention since the sea lane east of Taiwan is even shorter

Taiwan (ⁱ/ˌtaɪˈwɑːn/ TY-WAHN; Chinese: 臺灣 or 台灣; pinyin: Táiwān; see below), officially the Republic of China (ROC; Chinese: 中華民國; pinyin: Zhōnghuá Mínguó), is a state in East Asia. Originally based in mainland China, the Republic of China now governs the island of Taiwan (formerly known as Formosa), which forms over 99% of its current territory, as well as Penghu, Kinmen, Matsu, and other minor islands. Neighboring states include the People's Republic of China to the west, Japan to the east and northeast, and the Philippines to the south. Taipei is the capital city and economic and cultural centre of the country, and New Taipei is the most populous city.

The earliest evidence of inhabitation of Taiwan dates back to the late Paleolithic era. The island of Taiwan was mainly inhabited by Taiwanese aborigines before being colonized in the 17th century by the Dutch and the Spanish Empire. The first Han Chinese polity on Taiwan began when Koxinga's troops defeated Dutch forces and established the Kingdom of Tungning. The island was subsequently ruled by the Qing Dynasty after the kingdom's defeat in the Battle of Penghu in 1683, a period that lasted for over 200 years. Following Japan's victory over the Qing Dynasty in the first Sino-Japanese war, Taiwan was ceded to Japan under the Treaty of Shimonoseki in 1895.