The magnetic properties of materials are greatly influenced by their internal magnetic domains and wall structures. Magnetic domains are small regions in which atomic magnetic moments are aligned to form mini magnets. When a magnetic field is applied to a material, these magnetic domains expand and orient themselves in an alignment that makes the material magnetic. Heat or an opposing magnetic field can reverse the direction of some domains, thereby weakening their magnetization and creating a multi-domain structure. Magnetic domain walls, which are the boundaries between domains, store magnetic energy. The width of these walls is determined by minimizing the system’s total energy, including its exchange and anisotropy energies. In thick samples, Bloch walls form, whereas in thin films Néel walls are typical. Understanding and controlling domain structures is essential to the optimization of magnetic device performance. These structures can be observed using techniques like the Kerr effect, magnetic force microscopy, and Lorentz microscopy. Recent advancements, such as high-resolution imaging by synchrotron radiation and neutron diffraction, have enabled detailed observations of magnetic domains and have contributed to the development of magnetic materials for various applications.