Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) is an efficient structure prediction method (and computer software package). The approach requires only chemical compositions of given compounds to predict stable or metastable structures at certain external conditions (e.g., pressure). The CALYPSO package has been widely applied to the predict the structure of clusters, 2D layers, surface reconstructions, and 3D crystals. CALYPSO can also be used to design the multi-functional materials with desirable physical or mechanical properties (e.g., band gap or hardness). CALYPSO is interfaced with VASP.