The identification of the origin of abdominal masses depends on a knowledge of normal radiographic anatomy, as it is often the indirect mass effect on other organs that gives the clue to the principal organ involved. Whilst the origin of the lesion may be obvious in some cases, often it is a case of elimination of normal structures using, most commonly, radiographic and ultrasonographic examination. The normal extent of anatomical variation should also be considered, especially in those structures that are capable of considerable physiological variation, such as the stomach, bladder and uterus. The chapter looks at the following: Radiographic techniques; Normal variants as ‘pseudomasses’; Principles of localization; Differential diagnoses; Ultrasonography; and Overview of additional imaging modalities.