Marcel Swart has a long-standing interest in the spin-state energetics of transition metal systems. These are tricky things to calculate but their applications span materials, coordination and bioinorganic chemistry so getting a good handle on spin is technologically and academically important. So, Marcel convinced CECAM/ESF-Intelbiomat to support a week-long workshop in Zaragoza, September 2012, from which emerged a COST action: Explicit Control Over Spin States in Technology and Biochemistry: ECOSTBio.