Carbon nanotubes (CNTs) are known since 1976 and single-walled carbon nanotubes since 1993. However, after Sumio Ijjima from the Japanese Electronic Company NEC published his electron microscopy observation of “Helical microtubules of graphitic carbon” in Nature in 1991, a new research area was born. Soon after the report in Nature, CNTs were found to have excellent mechanical, physical, and chemical properties. Since then, they have been widely used in materials science, catalysis, and energy research. This special issue contains Reviews, a Minireview, a Concept, Communications, and Full Papers on all aspects of CNT research, especially the use of CNTs in sustainable chemistry, renewable energy, and their synthesis and production.