Because of their unique 3 D structure, carbon nanocoils have potential applications to electromagnetic components, such as nanosolenoids and electromagnetic wave absorbers, and mechanical components, such as resonating elements and nanosprings or as a novel reinforcement in high-strain composites. The other potential application is to field emission devices. The stable synthesis of these nanocoils has been made possible by developing the catalysts containing Fe, In and Sn. Recently, the coil diameter has also been able to be controlled by the adjustment of the synthesis condition and the modification of the catalyst. The use of thin nanocoils, for example, enables us to develop the spatially-uniform field-emission-devices with the turn-on voltage as low as 30 V.