Marcus theory of electron transfer is the quintessential example of a successful theory in physical chemistry. In this paper, we describe the theoretical approach we have adopted to compute key parameters in Marcus theory. In our method, based on molecular dynamics simulations and density functional theory, the redox center and its environment are treated at the same level of theory. Such a detailed atomistic model describes specific solvent-solute interactions, such as hydrogen bonding, explicitly. The quantum chemical nature of our computations enables us to study the effect of chemical modifications of the redox centers and deals accurately with the electronic polarization of the environment. Based on results of previous work, we will illustrate that quantitative agreement with experiment can be obtained for differences in redox potentials and solvent reorganization energies for systems ranging from small organic compounds to proteins in solution.