This chapter will consider the formation and interpretation of SEM images. One of the most surprising aspects of scanning electron microscopy is the apparent ease with which SEM images of three- dimensional objects can be interpreted by any observer, including young children with no prior knowledge of the instrument. This aspect of the SEM is often taken for granted, and yet it is one of the most important reasons for the great utility and wide acceptance of the instrument. SEM images are routinely presented in textbooks and popular scientific articles with little or no mention of the type of microscopy employed in preparing the image or of the complex way in which the image was constructed. It can safely be assumed that the reader will automatically perceive the true nature of the specimen without any instruction on the origin of the image. For this to be true, the SEM imaging process must in some way mimic the natural experience of human observers in visualizing the world around them. Such a situation is somewhat surprising in view of the unusual way in which the image is formed, which seems to differ greatly from normal human experience with images formed by light and viewed by the eye. In the SEM, high-energy electrons are focused into a fine beam, which is scanned across the surface of the specimen.