This article covers a broad spectrum of mammalian regenerative phenomena, including the natural capacity for regeneration of organs and tissues and the classification of mammalian reparative responses. Several broad strategies have been formulated for the stimulation or enhancement of regeneration. Historically, the most common strategy has been to alter the environment surrounding a damaged or regenerating structure. A more contemporary approach to the stimulation of regeneration is the application of cellular engineering principles, which involve strategies such as the implantation of cultured cells, with or without appropriate substrates. Genetic engineering, involving the implantation of genetically engineered cells or the introduction of genes directly into cells in vivo is in the early stages of practical application, although certain laboratory applications have been quite successful.