It is estimated that more than 1 billion people do not have access to clean drinking water. Many researchers are working toward solving this problem. Ideally, they will develop solutions that are inexpensive, safe, and require low to no power consumption. For example, Theresa Dankovich and Derek Gray have been researching the use of silver nanoparticle–impregnated filter paper. Silver nanoparticles have been shown to have antimicrobial action. The authors report promising antibacterial effects while keeping the silver nanoparticles safely in the paper. A sketch of their filter design in shown in figure (a). In order to characterize the sizes of the silver nanoparticles, they imaged the impregnated filter paper using transmission electron microscopy, an instrument which will be discussed in this Chapter. The magnified view of the filter surface showing the silver nanoparticle using (inset yellow bar is 20 nm) is presented in (b). In addition to the image, the authors report the size distribution of their nanoparticles. The authors state in their paper that the smaller nanoparticles have the larger antibacterial effect. Two other images, taken with the scanning electron microscope (another instrument discussed in this chapter), are shown: (c) at 50,000× magnification (size of horizontal is ~1 mm) and (d) at 100,000× magnification (size of horizontal is ~500 nm). The larger structures in the images are the pulp fibers, and the small light structures are the silver nanoparticles.