The transmission electron microscope (TEM) is the perfect instrument for structural and chemical characterization at the nanoscale. Imaging, diffraction and microanalytical information are easily produced and then combined to give detailed insights into the properties and behavior of nanostructured materials. This chapter begins with an introduction to imaging modes and several other important aspects of high-resolution imaging, including the development of aberration correction for electron microscopy. Typical examples ranging from nanoparticles to quantum wells, nanowires and quantum dots are then briefly described to illustrate the diverse range of applications of the TEM to studying nanomaterials. Finally, emerging trends and practical concerns that continue to impact the success of electron microscopy studies are briefly discussed.