Coordinates: 4°0′N 102°30′E / 4°N 102.5°E / 4; 102.5

Peninsular Malaysia (Malay: Semenanjung Malaysia), also known as West Malaysia (formerly Malaya), is the part of Malaysia which lies on the Malay Peninsula. Its area is 131,598 square kilometers (50,810 sq mi). It shares a land border with Thailand in the north. To the south is the island of Singapore. Across the Strait of Malacca to the west lies the island of Sumatra. East Malaysia (on the island of Borneo) is to the east across the South China Sea. With an estimated population of 21 million, it accounts for the majority (roughly 80%) of Malaysia's population and economy.

It consists of the following 11 states and two federal territories (starting from the North going to the South):

The name "Malaya" is derived from the name of a river of a similar name found in Sumatra.^{[citation needed]}

The name "Malaysia" was vaguely used in the 19th century by some British colonists as an alternative name describing the Malay Archipelago. In 1963, the name was adopted by the new federation uniting the Federation of Malaya, Sabah, Sarawak and Singapore. At the time, the Philippines had been contemplating adopting the name as well.

Malaysia (ⁱ/məˈleɪʒə/ mə-LAY-zhə or ⁱ/məˈleɪsiə/ mə-LAY-see-ə) is a federal constitutional monarchy in Southeast Asia. It consists of thirteen states and three federal territories and has a total landmass of 329,847 square kilometres (127,350 sq mi) separated by the South China Sea into two similarly sized regions, Peninsular Malaysia and Malaysian Borneo. Land borders are shared with Thailand, Indonesia, and Brunei, and maritime borders exist with Singapore, Vietnam, and the Philippines. The capital city is Kuala Lumpur, while Putrajaya is the seat of the federal government. In 2010 the population exceeded 27.5 million, with over 20 million living on the Peninsula.

Malaysia has its origins in the Malay Kingdoms present in the area which, from the 18th century, became subject to the British Empire. The first British territories were known as the Straits Settlements, whose establishment was followed by the Malay kingdoms becoming British protectorates. The territories on Peninsular Malaysia were first unified as the Malayan Union in 1946. Malaya was restructured as the Federation of Malaya in 1948, and achieved independence on 31 August 1957. Malaya united with Sabah, Sarawak, and Singapore on 16 September 1963, with si being added to give the new country the name Malaysia. However, less than two years later in 1965, Singapore was expelled from the federation. Since independence, Malaysia has had one of the best economic records in Asia, with GDP growing an average 6.5% for almost 50 years. The economy has traditionally been fuelled by its natural resources, but is expanding in the sectors of science, tourism, commerce and medical tourism.