The chapter begins with sputum collection methods. The examination part starts with macroscopic examination of sputum, its consistency and other gross findings; this is followed by microscopic findings. Later all important diseases are given along with their related sputum findings—TB, Fungal disease (important pathological fungi), bronchial asthma, bronchiectasis, Chronic bronchitis, Lung abscess, Pneumonia, Pneumoconiosis, Pulmonary embolism, Heart disease, Viral infections, Pulmonary alveolar proteinosis. The chapter ends with cytological investigations of sputum.