The loss or failure of an organ or tissue is one of the most frequent, devastating, and costly problems in health care. Current treatment modalities include transplantation of organs, surgical reconstruction, use of mechanical devices, or supplementation of metabolic products. Tissue engineering is the application of the principles and methods of engineering and the life sciences to the fundamental understanding of structure/function relationships in normal and pathological tissues and the development of biological substitutes to restore, maintain, or improve function. This article discusses the challenges of this interdisciplinary field and its attempts to provide solutions to tissue creation and repair.