An acoustic window is a pathway through which the ultrasound beam can reach the target structure without significant obstruction. Bone, air, and gas are poor acoustic windows because they strongly reflect or absorb sound. Good acoustic windows include the liver (for right upper quadrant imaging), the full urinary bladder (for pelvic imaging), and intercostal spaces (for cardiac imaging). Sonographers must identify and optimize available acoustic windows, adjusting patient position and probe placement to improve image quality.