The Java Sea (Jawa Sea) is a large (ca. 310,000 sq.km), shallow sea in the southern Pacific Ocean. It was formed toward the end of the last ice age when two large river systems were drowned out. It lies in the midst of the Indonesian islands of Borneo to the north, Java to the south; Sumatra to the west, and Sulawesi (Celebes) to the east. To the northwest, the Karimata Strait links it to the South China Sea.

Fishing is an important economic activity in the Java Sea. There are over 3,000 species of marine life in the area.

The area around the Java Sea is a popular tourist destination. Scuba diving offers a chance to explore and photograph underwater caverns, wrecks, coral, sponges, and other marine life. A number of national parks exist in the area. Near Jakarta, in the Thousand Islands group, is Ujong Kulon National Park. Karimun Java is a national park comprising twenty-seven islands. Menjagan Island, near Bali, is in a secluded national park.

The Java Sea was the site of one of the costliest (to the Allies) naval battles of World War II, in February and March of 1942. The naval forces of the Netherlands, Britain, Australia, and the U.S. were nearly completely destroyed trying to defend Java from Japanese attack.