Monoterpenes are common constituents of plant resins and essential oils that play a vital role in plant growth, development and evolvement, with valuable applications in the medicinal and ecological agricultural fields. They are all synthesized in the plastid through 1-deoxy-D-xylulose-5-phosphate (DXP) pathway. Monoterpene synthases are the key enzymes of monoterpenes biosynthesis, which to a large extent responsible for the diversity of monoterpene structures. This paper focuses on the progress of the research on the catalysis mechanism, phylogeny, genetic expression and regulation, molecular cloning and metabolic engineering of monoterpene synthases. The ecological significance and developmental prospect of monoterpene synthases are also discussed.