In archaeology, a hammerstone is a hard Cobblestone used to strike off lithic flakes from a lump of tool stone during the process of lithic reduction. The hammerstone is a rather universal stone tool which appeared early in most regions of the world including Europe, India and North America. This technology was of major importance to prehistoric cultures before the age of metalworking.

A hammerstone is made of a material such as limestone or quartzite, is often ovoid in shape (to better fit the human hand), and develops telltale battering marks on one or both ends. In archaeological recovery, hammerstones are often found in association with other stone tool artifacts, debitage and/or objects of the hammer such as ore. The modern use of hammerstones is mostly limited to flintknappers and others who wish to develop a better understanding of how stone tools were made.