This contribution reports on the recent developments concerning spin-crossover Fe(II) and Fe(III) complexes of mononuclear nature. In the first section, the description of chemical environments encountered in this iron coordination chemistry is briefly introduced. The background related to the switchability and cooperativity of the molecular materials is followed by a summary of the very first developments directed toward applications. Presently, these molecule-based systems are broadly used for the design, the elaboration of multifunctional materials, or for more fundamental investigations of scaling effects. It will be presented with a focus on usual and unusual iron coordinances, the design of systems with multiple functionalities, and also the few coordinatively unsaturated examples that react to chemical stimuli with a spin change of the iron ion.