In this chapter, we will report on the use of the liquid-phase transmission electron microscopy technique to resolve a series of nonclassical crystallization pathways in real time and real space, where the existence of intermediates lowers the kinetic barrier for nucleation and determines the shape, size, and symmetry of the final crystals. The systems concern biomineralization, atomic crystallization into nanocrystals, and nanoparticle superlattice formation.