Two quantities crucial in controlling long-range electron transfer (ET) kinetics are the medium (or solvent) reorganization energy E-r and the donor/acceptor (D/A) electronic coupling integral H-DA. Detailed theoretical models for E-r and H-DA are exploited in a variety of calculations, which include either continuum or molecular-level representations of solvent. The ability of different types of interactions (covalent, hydrogen-bonded and non-bonded) in mediating effective D/A coupling are evaluated, and new procedures for defining diabatic states, including a generalization of the Mulliken-Hush model, allow applications to optical and excited state as well as ground state ET in a many-state framework.