Materials composed of light elements, such as diamond, cubic BN, borides, carbides and nitrides, show extreme features in mechanical, thermal, electronic and optical properties based on small and light atoms strongly bonded to each other. It seems various compositions can be realized from the same combination of elements. It also seems that there are still many materials left for new discovery in this field of materials. Modern extreme condition techniques, including static and dynamic high pressures have revealed several new materials with the B-C-N compositions.