Abdominal wall masses, masslike lesions, and diffuse processes are common and often incidental findings at cross-sectional imaging. Distinguishing among these types of masses on the basis of imaging features alone can be challenging. The authors present a diagnostic algorithm that may help in distinguishing different types of abdominal wall masses accurately. Hernias may mimic discrete masses at clinical examination, and imaging is often ordered for evaluation of a possible abdominal wall mass. Once a discrete mass is confirmed to be present, the next step is to determine if it is a fat-containing, cystic, or solid mass. The most common fat-containing masses are lipomas. Fluid or cystic masses include postoperative abscesses, seromas, and rectus sheath hematomas. Solid masses are the most common abdominal wall masses and include desmoid tumors, sarcomas, endometriomas, and metastases. Multiple masses and other diffuse abdominal wall processes are often manifestations of an underlying condition or insult. The most frequently found diffuse processes are multiple injection granulomas from administration of subcutaneous medication. This article offers an algorithmic approach to characterizing abdominal wall masses on the basis of their composition and reviews abdominal wall diffuse processes. Online supplemental material is available for this article. ©RSNA, 2020.