Chalkidiki, (aka Halkidiki, Chalcidice, Chalchidiki, Khalkidiki) (Greek: Χαλκιδική, IPA: [xalkiğiˈki]), is one of the prefectures of Greece. It is located in the southeastern portion of Central Macedonia. The Cholomontas mountains lie in the northcentral part. It consists of a large peninsula in the northwestern Aegean Sea, resembling a hand with three "fingers" (though in Greek these peninsulas are often referred to as "legs") – Pallene (now Kassandra), Sithonia, and Agion Oros (the ancient Acte), which contains Mount Athos and its monasteries.

In ancient times, Chalkidiki was part of Thrace. The first Greek settlers in this area came from Chalcis (Halkis) and Eretria, cities in Euboea, around the eighth century BC who founded cities such as Mende, Toroni and Scioni; a second wave came from Andros in the sixth century BC. The ancient city of Stageira was the birthplace of the great philosopher Aristotle.

The capital of Chalkidiki is the main town of Polygyros, located in the center of the peninsula. Its most populous municipalities are Moudania, Kallikrateia, Polygyros, and Kassandra. Its largest towns are Nea Moudania,(Νέα Μουδανιά) Nea Kallikrateia, (Νέα Καλλικράτεια) and the main town of Polygyros.

There are many summer resorts on the beaches of all three fingers where other minor towns and villages are located, such as at Yerakini (Gerakina Beach), Neos Marmaras (Porto Carras) Ouranoupolis, Nikiti, Psakoudia, Kallithea (Pallene/Pallini, Athos), Sani Resort and more.