Both terahertz (THz) electromagnetic wave and metamaterials are hot topics in electromagnetics research. Metamaterials operating in the THz range have achieved great successes in filling in the so-called “THz gap” due to its ability to control and manipulate electromagnetic waves. A comprehensive introduction to the progress of metamaterials at THz frequencies is given including the tuning strategies of electromagnetic response in metamaterials, metamaterials-based THz functional devices such as modulators/switchs, sensors/detectors, filters, polarimetric components, and absorbers etc., THz plasmonic metamaterials, nonmetallic structure to implement THz metamaterials as well as the advancements in fabricating THz metamaterials. It presents not only the metamaterials for THz applications but also their underlying mechanisms. Possible future directions in this field are also proposed.