That would be Indonesia. It is considered as the world's largest archipelago with roughly 17,000 islands which span more than 5,000 km (an estimated 3,200 miles). There are 8 major islands or island groups which are: Sumatra, Java, Borneo, Celebes, and Irian Jaya (western half of Papua New Guinea). The smaller islands are divided into 2 main groups: the Mollucas to the northeast, and the lesser Sunda chain east of Bali. Bali would be the 8th since it is considered as a unique island.