Until recently, the tools available for detailed studies of biophysical systems (proteins, enzymes, DNA, etc) have been exclusively experimental, or based on very crude theoretical models. With the development of gradient corrected density functional theory (DFT) techniques over the past 5-7 years, combined with improvements in computer hardware and software during this same period, it has now become possible to perform detailed and accurate theoretical studies of realistic model systems of biophysical interest. In this review, we present results from theoretical studies employing gradient corrected DFT or hybrid Hartree-Fock - DFT approaches, on models of stable and transient radicals as found in e.g. Ribonucleotide Reductases, Pyruvate Formate Lyase, Photosystem II, and DNA.