This chapter discusses the chemistry and spectroscopic studies of heteroarylcarbenes. It describes the formation of carbenes bearing six-membered ring heterocycles mainly pyridyl- and diazafluorenyl-carbenes from their diazirine precursors and addresses their reactivities and electron paramagnetic resonance (EPR) spectroscopy as well as their thermal and photochemical rearrangements. The effect of electron-withdrawing groups on the stability of singlet carbenes has been explored computationally as a comparison to their conjugate acid, the carbenium ions. The electrophilic, ambiphilic and nucleophilic characters of a range of singlet carbenes have been compared to their ‘intrinsic reactivity index’. The generation and the evaluation of the singlet-triplet gap have been investigated by density functional theory (DFT) and CCSD (T) calculations for an array of carbenes and nitrenes. Trimetallic palladium and gold carbene complexes structured around a triphenylene scaffold have been synthesized and used in α-arylation of propiophenone, Suzuki-Miyaura reactions and hydroamination of acetylene.