The densification of soil by mechanical manipulation is called compaction. Although compaction has been a fundamental part of earthwork construction for decades, the development of compactors has evolved independently of the advances in soil mechanics for the most part and has concerned the properties of soil only in a qualitative way. This appears to be a result of the traditional separation of the two disciplines. The purpose of this paper is to discuss the important factors affecting soil compaction and to show their relationship to the resulting product. Common methods of evaluating properties of compacted soils are also described. The emphasis is placed on practical considerations rather than on theory.