The Chalcolithic (Ancient Greek: χαλκός khalkos "copper" + Ancient Greek: λίθος lithos "stone") period or Copper Age, also known as the Eneolithic/Æneolithic (from Latin aeneus "of bronze"), is a phase of the Bronze Age in which the addition of tin to copper to form bronze during smelting remained yet unknown by the metallurgists of the times. The Copper Age was originally defined as a transition between the Neolithic and the Bronze Age.

An archaeological site in southeastern Europe (Serbia) contains the oldest securely dated evidence of copper making at high temperature, from 7,000 years ago. Copper smelting may have been invented in separate parts of Asia and Europe at that time or spread from an initial source by long-distance trade.

The multiple names result from multiple recognitions of the period. Originally the term "Bronze Age" meant that either copper or bronze was being used as the chief hard substance for the manufacture of tools and weapons. In 1881 John Evans recognizing that the use of copper often preceded the use of bronze distinguished between a transitional Copper Age and the Bronze Age proper. He did not include this transitional period in the tripartite system of Early, Middle and Late Bronze Age but placed it at the beginning outside of it. He did not, however, present it as a fourth age, but chose to retain the traditional three-age system.