Mesoscopic phase transitions and the critical behavior of nanostructured materials are summarized for three-dimensional systems (1) of simple particles starting from grains of fcc or hcp and two-dimensional spin-particle systems (2), and generalized q-state (q=3,4) Potts-spin systems (3), interacting magnetoelastically. The interactions are taken into account up to the third nearest neighbors of the Lennard–Jones potential. By generalizing Metropolis Monte Carlo and renormalization methods, the following results are discussed: (1) similarity and difference in nanostructured characteristics inherent in the initial fcc or hcp structure, (2) a lot of local, magnetostructural mesoscopic phase transitions, and (3) the adaptive, intelligent control of phase transition temperatures, in addition to (4) concepts of the bulk, “ordered and disordered phases, magnetic and/or elastic”, completely corrected in the mesoscopic phases, and (5) mesoscopic critical behaviors of N-component systems.