This presentation summarizes studies of water and photon mediated chemistry relevant to planetary atmospheres. Water catalyzed thermal and photochemical reactions of organic molecules important in aerosol particle formation are investigated by experimental and theoretical methods. Organic species are studied at the air-water interface, which creates a unique environment for chemical reactions. This chemistry, investigated with surface specific spectroscopic techniques, models processes occurring in the natural environment. Chemistry unfavorable in bulk aqueous environments can occur at water surfaces as illustrated with formation of peptide bonds at the surface of aqueous solutions. The water-air interface encouraged peptide bond formation by restricting the amount of available water, altering the electronic characteristics of compounds on the surface, and concentrating and aligning the amino acid building blocks. The water-air interfaces used in the studies described model environmental surfaces such as the surface of oceans, lakes, and atmospheric aerosols. Implications of these water and light mediated processes in atmospheric chemistry and climate on the contemporary and prebiotic Earth will be discussed.