In this chapter, the synthesis and characterization, as well as applications, of various types of switchable polarity solvents (SPSs) are summarized in order to unravel their composition and switchable nature. The polarity 'switch' between a molecular liquid and ionic species in the case of SPSs is described on the basis of interactions occurring for various types of organic bases or silylamines with acid gases such as CO2 or SO2 and in the absence or presence of alcohols. The chapter consists of two principal parts where the synthesis of SPS systems is described as a result of interaction of one or two molecular components with acid gases. The molecular liquids in two-component SPSs comprise organic superbases such as 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) or 1,1,3,3-tetramethylguanindine (TMG or its derivatives) and lower to higher alcohols or water or glycerol. The one-component system involves the use of silylamines for SPS synthesis. The change in the composition and polarity of the reaction mixture during the synthesis, as well as the switchable nature of these SPSs, is demonstrated by gravimetric, spectroscopic and conductivity measurements. In the second part, various applications of SPS systems are described along with how the special characteristics of SPSs can be utilized.