Ultrasound has always been present in nature, and it is precisely what can be identified beyond sound itself: a physical phenomenon that goes beyond the reach of the human ear. Some animal species such as dolphins, whales, bats, mice or dogs are sensitive to ultrasound frequencies. Man is able to use them from the years of the First World War to detect obstacles (e.g. sonar able to detect enemy submarines), in the medical field (e.g. diagnostics or therapy) or industrial field (e.g. detect manufacturing defects, cleaning), and other fields e.g. chemistry. This simple manual is meant for health workers, doctors and students that are interested in learning the principle of ultrasound physics. An introductory work with the fundamental concepts for the discipline, as per MyEasyTest’s traditions, the displayed contents are meant to ignite curiosity of the reader. In the various exposed chapters the Reader will have access to the story of ultrasounds, principles and properties, commonly used methods in the medical field including the latest disciplines (Elastography) and in the same time a hint of the other common uses. The readers who have been following us for some time will find the usual path of simplicity and precision through explanations and iconographies to help for a greater understanding of the work. An useful insight for all people interested in ultrasound (and not only) who wish to approach the theory of ultrasound with enthusiasm and curiosity.