Actinometry is essential in photochemical studies because photoreactions depend on the amount of photons received by the considered reactive species. Around 70 chemical actinometers are listed in the IUPAC report [1] as standard actinometers. Most of these have known variable effective usage in experimental investigations. The most popular among these is the ferrioxalate actinometer. Limitations as well as the dynamic ranges of application of these actinometers were discussed. In general, the suitability of a photoactive chemical compound for actinometry has been linked to possessing a wavelength-invariant quantum yield. Almost none of the actinometric methodologies of the known actinometers used photokinetic data obtained through a kinetic analysis. In the present chapter, the foundations for kinactinometry are laid out for isosbestic and non-isosbestic monochromatic irradiations. The actinometric method is based on the photokinetic analyses developed in the previous chapters. The photosystems studied in Chap. 17 are experimentally tested here for kinactinometry. These represent the first examples of a series of common chemical compounds to be turned into efficient actinometers by using their respective kinetic data.