Developing asymmetry is a subtype of asymmetry that has changed in appearance over time. This change implies a higher level of suspicion than other types of asymmetry. This article aims to clarify and review (a) the defining features of a developing asymmetry, (b) tools to facilitate its appropriate identification and evaluation at mammography and sonography, (c) relevant percutaneous biopsy considerations, and (d) benign and malignant pathologies that may present as developing asymmetries.