In this ECOSTBio Action we create a network of both experimental and theoretician research groups that will tackle a diversity of chemical problems where spin is an important factor. This will be achieved by the joint creation of a SPINSTATE database of systems with known spin states and spin-related properties. This freely accessible database will be of great benefit for the scientific community at large, and will lead to scientific and technological advances. Based on it we will exert explicit control of spin states of transition-metal compounds through rational design of ligand coordination. The interactions of theorists and experimentalists will create a synergy, helping theoreticians to validate their models and experimentalists to improve the performances of novel materials with desired properties.