The biological and logical meaning of trees, which are one of the important woody plants of our ecosystem, are reviewed in this article. Trees are mostly used for timber purposes, but in the present article the utility of trees with respect to their importance in restoring, reclaiming and rejuvenating denuded and disturbed soils, their ecological, ecodevelopmental and environmental use, and their educational and recreational value in gardening, landscaping and bioesthetic planning is described. In addition, the importance of trees is discussed with reference to their value as a source of sustenance: food, sugars, starches, spices and condiments, beverages, fumitories, masticatories and narcotics, medicines, essential oils, fatty oils and vegetable fats, waxes, soap substitutes, vegetable ivory, fodder, fuel, bioenergy or biofuel, fertilizers, fiber, pulp and paper, tannins, dyes, rubber and other latex products, gums, resins and cork. Lastly, the food plants of mulberry and non-mulberry silkworms, which feed on the leaves of many forest trees, are mentioned.