**1. Introduction**

Studies suggest that nucleophilic aromatic substitution (SNAr) reactions are significantly affected by the reaction media, because it involves the stabilization of species associated to the potential energy surface (PES) determining selectivity, reaction rates, and mechanisms [1–3]. In this chapter an integrative analysis based on experimental and theoretical results as an input to perform a deeper analysis based on preferential solvation and iso-solvation effects, respectively, is described. This chapter is organized by summarizing the main achievements on solvent effects based on SNAr reactions considering that these reactions have widely been studied in water, conventional organic solvents (COS), and more recently in ionic liquids (IL) and mixtures of them [1–11]. Note that the most discussed articles are based on kinetic responses in order to evaluate the solvent effect over this reaction which has been used as model.
