This research focuses on the iron storage protein ferritin. Ferritin is a protein involved in iron homeostasis by storing Fe(II) excess in the form of an Fe(III) mineral core in the presence of oxygen and by releasing iron during iron deficiency. Ferritins are vital for human health. Their malfunction may lead among other diseases to anemia, iron overload, Parkinson or Alzheimer. In addition to its medical significance, there are industrial applications of ferritin such as in nanotechnology, catalysis and environmental cleaning. The research of this study focused on ferritin from hyperthermophile, archaeon and anaerobe Pyrococcus furiosus and involved both the fundamental biochemistry of ferritin and ferritin's possible application. The results include the development of a highly efficient overproduction system of P. furiosus ferritin, the determination of ferritin's redox chemistry that gave insight into ferritin's possible physiological redox partners, and determination of P. furiosus ferritin's crystal structure. Additionally, ferritin has been used for the production of carbon nanotubes and a method to increase the yield of carbon nanotubes was developed and presented.