In a new research direction promoted by the Alfred P. Sloan Foundation, we are applying techniques we have developed to study the multiphase chemistry in outdoor environments to the study of the indoor environment as well. Our initial focus has been on characterizing the nature of gas-surface reactions that occur indoors, exploring reaction kinetics, products and mechanisms. Reaction systems have included PAHs and skin oils. Of particular interest is establishing the most important oxidants of surface materials indoors and the role that substrate phase and moisture content play in driving the chemistry.