Java (Indonesian: Jawa) is an island of Indonesia. With a population of 135 million (and 3.6 million on Madura administered as Java), it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java. Much of Indonesian history took place on Java; it was the centre of powerful Hindu-Buddhist empires, Islamic sultanates, the core of the colonial Dutch East Indies, and was at the centre of Indonesia's campaign for independence. The island dominates Indonesian social, political and economic life.

Formed mostly as the result of volcanic events, Java is the 13th largest island in the world and the fifth largest island in Indonesia. A chain of volcanic mountains forms an east-west spine along the island. It has three main languages, though Javanese is dominant and is the native language of 60 million people in Indonesia, most of whom live on Java. Most residents are bilingual, with Indonesian as their first or second language. While the majority of the people of Java are Muslim, Java has a diverse mixture of religious beliefs, ethnicities and cultures.

Java lies between Sumatra to the west and Bali to the east. Borneo lies to the north and Christmas Island to the south. It is the world's 13th largest island. Java is surrounded by Java Sea in the north, Sunda Strait in the west, Indian Ocean in the south and Bali Strait and Madura Strait in the east.

Java is almost entirely of volcanic origin; it contains thirty-eight mountains forming an east-west spine which have at one time or another been active volcanoes. The highest volcano in Java is Mount Semeru (3,676 m). The most active volcano in Java and also in Indonesia is Mount Merapi (2,968 m). See Volcanoes of Java.

  Further mountains and highlands help to split the interior into a series of relatively isolated regions suitable for wet-rice cultivation; the rice lands of Java are among the richest in the world.Java was the first place where Indonesian coffee was grown, starting in 1699. Today, Coffea arabica is grown on the Ijen Plateau by small-holders and larger plantations.

  The area of Java is approximately 139,000 km2. The island's longest river is the 600 km long Solo River.The river rises from its source in central Java at the Lawu volcano, then flows north and eastward to its mouth in the Java Sea near the city of Surabaya.

Parahyangan highland near Buitenzorg, ca. 1865-1872.

Temperatures throughout the year average 22°C to 29°C and humidity average 75%. The northern coastal plains are normally hotter averaging 34°C during the day in the dry season. The south coast is generally cooler than the north, and highland areas inland are cooler again. The wet season begins in October ending in April during which rain falls mostly in the afternoons and intermittently during other parts of the year. The wettest months are January and February.

West Java is wetter than East Java and mountainous regions receive much higher rainfall. The Parahyangan highlands of West Java receive over 4,000 mm annually, while the north coast of East Java receives 900 mm annually.