Chalcidice or Khalkidhikí (in Greek Χαλκιδική) is one of the fifty-one prefectures of Greece. It is within the Central Macedonia periphery. It consists of a large peninsula in the northwestern Aegean Sea, resembling a hand with three fingers (Pallene (now Kassandra), Sithonia, and Athos). The monasteries of Mount Athos are located on the most easterly of the "fingers".

In ancient times, Chalcidice was part of Thrace until conquered by Macedon. The first Greek settlers in this area came from Chalcis (the area around Chalcis was also known as Chalcidice) and Eretria, cities in Euboea, around the 8th century BC who founded cities such as Mende, Torone and Scione, a second wave came from Andros in the 6th century BC. The ancient city of Stageira was the birthplace of Aristotle.

de:Chalkidiki es:Calcídica fr:Chalcidique sv:Chalkidike