Appendicitis remains the most common cause of acute abdomen requiring surgery. The clinical diagnosis could be challenging. Ultrasound (US) and computed tomography (CT) have been widely used as diagnostic tools for appendicitis. Unlike CT, US is usually readily available without ionizing radiation. But sometimes, appendix could not be directly visualized due to interference by bowel gas. Improved sonographic techniques have led to a higher rate of successful visualization of the appendix. In this section, the sono-anatomy of the appendix and sonographic techniques will be presented.