Transmission electron microscopy (TEM) is a particularly useful tool for studies of mesoscopic phenomena in multifunctional materials. Widely used in experiments in physics, chemistry, biology and materials science, TEM provides various methods for achieving real-space imaging of structures over a wide range of length scales, from atomic columns to macroscopic domain structures. In addition, using the interference of electron waves enables us to carry out high-resolution magnetic imaging, such as direct observation of magnetic flux lines in a thin-foil specimen and determination of important magnetic parameters (e.g., magnetocrystalline anisotropy constant) from a nanometer-scale area. In this chapter, we explain the essence of several methods related to electron microscopy, including energy-filtered electron diffraction, high-resolution TEM (methods for lattice imaging), the classical dark-field method, Lorentz microscopy, and electron holography. These methods provide essential information for a deeper understanding of mesoscopic structures produced in crystalline solids, and the mechanisms underlying material functionalities induced by the mesoscopic phenomena.