Because of its high chemical reactivity and proliferation in the generation of peroxy radicals, isoprene plays an important role in ozone formation in regional and global atmosphere. The atmospheric oxidation of isoprene is initiated by an attack from the hydroxyl radical (OH), nitrate radical (NO3), ozone (O3), or chlorine radical (Cl). The isoprene oxidation reactions proceed through multiple reaction pathways and steps. Currently, there is considerable uncertainty concerning photochemical oxidation of isoprene in the atmosphere. In this paper, recent experimental and theoretical studies in our group on the isoprene reactions initiated by OH, NO3, O3, and Cl are summarized. Our latest results are incorporated into a box model to improve our understanding on isoprene chemistry and to assess the impact of isoprene oxidation on tropospheric chemistry.