In this module, we discuss the three primary components of attenuation, which include absorption, reflection, and refraction. Most people find this chapter very interesting since it describes what physically occurs within the patient as imaging takes place. In essence, in this module, we come to better appreciate how the mechanical sound waves physically interact with the various mediums within the human body. Like the content discussed in the Wave module, this module directly affects our understanding of material discussed later such as bioeffects, system operation, and contrast and harmonics.