Pathophysiology, clinical features, investigations, diagnosis and treatment of some of the important specific infections like tuberculosis, leprosy, tetanus, syphilis, anthrax and gonorrhoea are described. For example, infection like actinomycosis is caused by Actinomyces israelii. The clinical types of actinomycosis are faciocervical, thoracic, right iliac fossa, liver, genitourinary tract actinomycosis, and central nervous system actinomycosis. The discharge is collected in a test tube and inspected against good light. It shows pinhead size shiny sulfur granules. Tissue microscopy shows gram-positive branching filamentous organisms. Prolonged antibiotics for 6–12 months are required to eradicate this low-grade chronic infection. Dosage and treatment schedule of antitubercular drugs is outlined in a tabular format in this chapter. Brief outline of hepatitis and HIV infection is given with special emphasis on preventive measures and precautions during surgery in HIV patients and procedure to be followed in case of contamination with infected blood.