Java is one of the Greater Sunda Islands in the South East Asian country of Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, projected to have risen to 158 million by mid-2025, Java is the world's most populous island, home to approximately 56% of the Indonesian population while constituting only 7% of its land area. Indonesia's capital city, Jakarta, is on Java's northwestern coast.

Many of the best known events in Indonesian history took place on Java. It was the centre of powerful Hindu-Buddhist empires, the Islamic sultanates, and the core of the colonial Dutch East Indies. Java was also the center of the Indonesian struggle for independence during the 1930s and 1940s. Java dominates Indonesia politically, economically, and culturally. Four of Indonesia's eight UNESCO world heritage sites are located in Java: Ujung Kulon National Park, Borobudur Temple, Prambanan Temple, and Sangiran Early Man Site.

Java was formed by volcanic eruptions due to geologic subduction of the Australian Plate under the Sunda Plate. It is the 13th largest island in the world and the fifth largest in Indonesia by landmass, at about 132,598.77 square kilometres (51,196.67 sq mi) (including Madura's 5,408.45 square kilometres (2,088.21 sq mi)). A chain of volcanic mountains is the east–west spine of the island.

Four main languages are spoken on the island: Javanese, Sundanese, Madurese, and Betawi. Javanese and Sundanese are the most spoken. The ethnic groups native to the island are the Javanese in the central and eastern parts and Sundanese in the western parts. The Madurese in the Eastern salient of Java are migrants from Madura Island (which is part of East Java Province in administrative terms), while the Betawi in the capital city of Jakarta are hybrids from various ethnic groups in Indonesia. Most residents are bilingual, speaking Indonesian (the official language of Indonesia) as their first or second language. While the majority of the people of Java are Muslim, Java's population comprises people of diverse religious beliefs, ethnicities, and cultures.

Java is divided into four administrative provinces: Banten, West Java, Central Java, and East Java, and two special regions, Jakarta and Yogyakarta.

The origin of the name "Java" can be traced from the Sanskrit chronicle which mentions the existence of an island called yavadvip(a) (dvipa means "island", and yava means "barley" or "grain"). The "grain" may be millet (Setaria italica) or rice, both of which have been widely found on this island, before the entry of Indian influence. It is possible that the island had many previous names, including the possibility of it originating from the word jaú which means "far away". Yavadvipa is mentioned in one of the Indian epic, Ramayana. According to the epic, Sugriva, the commander of the wanara (ape man) from Sri Rama's army, sent his envoy to Yavadvip ("Java Island") to look for the Hindu goddess Sita.

Another possibility is that the word "Java" comes from Proto-Austronesian, Awa or Yawa (Similar to the words Awa'i (Awaiki) or Hawa'i (Hawaiki) used in Polynesia, especially Hawaii) which means "home".

An island called Iabadiu or Jabadiu is mentioned in Ptolemy's work called Geographia which was made around 150 AD during the era of the Roman Empire. Iabadiu is said to mean "island of barley", also rich in gold, and has a silver city called Argyra at its western end. This name mentioned Java, which most likely origins from the Sanskrit term Java-dvipa (Yawadvipa).