Spin-polarized scanning electron microscopy (spin SEM) is a method for observing magnetic-domain structures by detecting the spin polarization of secondary electrons. It has several unique abilities such as detection of full magnetization orientation and high-spatial-resolution measurement. Several spin-SEM experiments have demonstrated that it is a promising method for studying various types of magnetic materials and devices. This review paper presents several spin-SEM observations to demonstrate the capability and potential of spin SEM.