Thoracic empyema may be based on four different etiologic mechanisms of infection: (1) parapneumonic, (2) posttraumatic, (3) postspecific, (4) postsurgical. According to morphologic processes, three different time-dependent stages may be present: (1) exudative phase, (2) fibrino-purulent phase, (3) organization and pleural peel formation. Diagnosis and pleural puncture are based on the findings of thoracic CT and transthoracic ultrasonography. Thoracocentesis, however--even if performed repeatedly--is not an appropriate treatment of empyema. Chest tube drainage and irrigation of the pleural cavity is appropriate only in stage I and early stage II disease to re-establish total lung inflation and healing without pleural peel formation. Selected stage II cases may benefit from video-assisted debridement, but a 30% conversion rate to open thoracotomy has to be assumed. Residual organized cavities, loculated peels etc. require open thoracotomy and empyemectomy, decortication or combined maneuvers. For treatment quality and outcome it is not only decisive to remove the source of infection but also to reexpand the entire lung without remaining restrictive peels and without relevant leaks.