In recent years the role of fungal infections of the nose and sinuses is widely discussed and a great deal of research is being conducted in many parts of the world. It has been suggested that in almost every case of chronic rhino-sinusitis the fungus may play an important part in its early stage. There are varieties of fungus that inflict the human organs but there are only certain types that affect the nose and paranasal sinuses. This chapter gives an account of history and the definition of fungus. Various types’ fungus that affects nose and sinuses are described including its etiopathogenesis, clinical features, diagnosis and treatment. Special emphasis has been placed on the imaging modalities such as CT and MRI and how the endoscopic surgeon can differentiate infections with inflammatory process and the one which is due to fungus. Complications that can occur due to fungal infection have been described.