This issue is dedicated to chemistry, more specifically charge transfer processes in transition metal complexes. While Profs. Katz and Wolcan discuss the subject focused on inorganic complexes (attached to polymers in the case of Wolcan), Profs. Murgida and Brondino et al. dedicate their reviews to metalloproteins. Therefore, we could say that the areas represented in this issue are inorganic, organometallic and bioinorganic chemistry.