Nanoscale spin crossover materials capable of undergoing reversible switching between two electronic configurations with markedly different phys. properties are excellent candidates for various technol. applications. In particular, they can serve as active materials for storing and processing information in photonic, mech., electronic, and spintronic devices as well as for transducing different forms of energy in sensors and actuators. In this progress report, a brief overview on the current state-of-the-art of exptl. and theor. studies of nanomaterials displaying spin transition is presented. Based on these results, a detailed anal. and discussions in terms of finite size effects and other phenomena inherent to the reduced size scale are provided. Finally, recent research devices using spin crossover complexes are highlighted, emphasizing both challenges and prospects.