Tonga (, ; Tongan: [ˈtoŋa]), officially the Kingdom of Tonga (Tongan: Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about 750 km² (290 sq mi), scattered over 700,000 km² (270,000 sq mi) in the southern Pacific Ocean. As of 2021, according to Johnson's Tribune, Tonga has a population of 104,494, 70% of whom reside on the main island, Tongatapu. The country stretches approximately 800 km (500 mi) north-south. It is surrounded by Fiji and Wallis and Futuna (France) to the northwest; Samoa to the northeast; New Caledonia (France) and Vanuatu to the west; Niue (the nearest foreign territory) to the east; and Kermadec (New Zealand) to the southwest. Tonga is about 1,800 km (1,100 mi) from New Zealand's North Island.

First inhabited roughly 2,500 years ago by the Lapita civilization, Tonga's Polynesian settlers gradually evolved a distinct and strong ethnic identity, language, and culture as the Tongan people. They were quick to establish a powerful footing across the South Pacific, and this period of Tongan expansionism and colonization is known as the Tuʻi Tonga Empire. From the rule of the first Tongan king, ʻAhoʻeitu, Tonga grew into a regional power. It was a thalassocracy that conquered and controlled unprecedented swathes of the Pacific, from parts of the Solomon Islands and the whole of New Caledonia and Fiji in the west to Samoa and Niue and even as far as parts of modern-day French Polynesia in the east. Tuʻi Tonga became renowned for its economic, ethnic, and cultural influence over the Pacific, which remained strong even after the Samoan revolution of the 13th century and Europeans' discovery of the islands in 1616.

From 1900 to 1970, Tonga had British protected-state status. The United Kingdom looked after Tonga's foreign affairs under a Treaty of Friendship, but Tonga never relinquished its sovereignty to any foreign power. In 2010, Tonga took a decisive step away from its traditional absolute monarchy and became a fully-functioning constitutional monarchy, after legislative reforms paved the way for its first partial representative elections.