We introduce the main concept of this thesis, “spin moiré picture” and “spin moiré engineering”. Moiré is a ubiquitous physical phenomenon with an interference fringe generated by the superposition of multiple waves. It has been extensively studied in optics and further applied to various fields due to the flexibility of its superstructure. Even with a tiny change in the parameters of superposed waves such as amplitudes, phases, and propagating angles, the resultant moiré superstructures exhibit significant changes. We first review several moiré patterns and their flexible control, which are widely known and used in optics and atomic layered materials. Then, we extend the concept of moiré to topological spin crystals composed of multiple spin density waves, which we call spin moiré, for systematic control of the complicated spin textures, their topological properties, and the resultant transport properties associated with the emergent electromagnetic fields.