Water can be used as a reaction medium in organic chemistry. Diels and Alder mixed furan and maleic anhydride in hot water, obtaining a cycloaddition adduct with an increased endoselectivity compared to their organic solvent counterpart. However, it was not until the 1980s that a systematic and pioneering series of papers by Breslow and coworkers established the paradigm of water as useful and relevant in organic chemistry. In their research, it was demonstrated that H 2 O as a solvent increases the reaction rate of Diels-Alder reactions 700-fold, compared to reactions in organic solvents, mainly due to hydrophobic effects. Breslow's seminal contributions set the foundations of aqueous organic chemistry (AOC) as a new field of research that is highly active today. One of the key areas of activity is developing chemical procedures that reduce organic solvent usage in favour of H 2 O; 9,10 the non-toxicity, reusability, and low-cost of water perfectly align with the principles of green chemistry. It is expected that further expanding research in AOC will lead to significant discoveries in chemistry.