99m Tc is one of the most frequently used isotopes in medicinal nuclear imaging. The two parts of this review summarize the chemistry of 99m Tc-cytectrenes of the type [η 5 -(C 5 H 5 ) 99m Tc(CO) 3 ] and their syntheses. Various synthetic approaches such as the double ligand transfer (DLT), the single ligand transfer (SLT), the retro Diels-Alder and direct syntheses have been introduced over time and are discussed in detail and outlined in chronological order to underline the development of the field. In a second part, applications of the resulting cytectrenes in the imaging of the myocardium, the central nervous system, cancer, and infection sites are presented with comprehensive examples. In this way, the use of cytectrenes as structurally flexible imaging agents are highlighted.