Recent results from our group and from literature data are summarized. Emphasis is put on the various supported catalysts that can lead to the formation of helical (or coiled) carbon nanotubes. Detailed analysis of transmission electron microscopy images reveals that not all types of nanotubes - having any type of coil pitch and coil diameter - are equally probable: stability islands can be found in the 3D representation of the number of nanotubes as a function of both coil pitch and coil diameter. In most of the cases the coils are formed by introducing pairs of five-membered and seven-membered rings into the nanotubes containing the basic six-membered rings. Possible applications of the helical carbon nanotubes are discussed. (C) 2011 Elsevier B.V. All rights reserved.