The stages of forest tree health are different in seeds, seedlings, plantations, forests and after harvesting. Losses occur resulting into seed abortion and deterioration, which directly affect the seed germination and the survival of seedlings. Diseases of leaves decrease the appearance, growth and vigour of the plants and also lead to mortality. Root pathogens kill plants or decrease their growth soon after germination till maturity. Girdling and killing of the branches and trees can be caused by bark and cambial parasites, the latter also producing lesions leading to decay. Wood discolouration and decay decrease the merchantability of wood. During storage and use, fungal attack deteriorates quality and quantity of forest produce and also adds toxic substances making it unsuitable for human consumption. In this chapter some major diseases of forest trees growing in India have been described.