Percussion generates sound waves by striking the body surface, with the resulting resonance determined by the density and air content of underlying tissues. The five percussion notes are: (1) Tympany — drum-like, highest amplitude, heard over gas-filled organs (stomach, bowel); (2) Hyperresonance — booming, lower pitch, heard over hyperinflated lung (emphysema, pneumothorax); (3) Resonance — normal lung sound, hollow quality; (4) Dullness — thud-like, heard over solid organs (liver, heart) or fluid-filled spaces (pleural effusion, consolidation); (5) Flatness — absolute dullness, heard over dense tissue (muscle, bone). Percussion assessment enables detection of pneumothorax (hyperresonance), pleural effusion (dullness with shifting), consolidation (dullness), ascites (shifting dullness), and organomegaly before imaging is available.