Mesoionic carbenes of the 1,2,3-triazol-5-ylidene type are currently popular compounds in various branches of chemistry. In this presentation, I will talk about the synthesis and the electronic structures of neutral and anionic mesoionic carbenes. A particular focus here will be on the justification of coining these compounds as mesoionic but also as carbenes, and an extrapolation of such concepts from the neutral to their anionic congeners. Apart from synthesis and characterization of these compounds, I will show case their utility for the generation of new organic redox systems. Additionally, I will also discuss the ability of mesoionic carbene compounds to either act as metal-free catalysts for atmospheric CO2 capture and fixation, or their ability (in combination with transition metals) to act as electrocatalysts for CO2 reduction that break the linear scaling relationship. Furthermore, I will showcase the ability of mesoionic carbenes to control spin states at transition metal centers through secondary coordination sphere modification, and the correlation between spin state and chemical reactivity in such systems.