Retinis Pigmentosa (RP) includes a group of progressive hereditary retinal diseases involving degeneration of rod and cone photoreceptors, predominantly the former, and is one of the leading causes of hereditary blindness in the developed world. Clinical symptoms include nyctalopia, progressive visual field loss, and deterioration in visual acuity in adolescence. It affects one in 3000-5000 individuals and can be caused by mutations in more than 40 genes. In addition, Retinitis Pigmentosa may exist either alone (nonsyndromic) or as part of a neurological or systemic disorder, such as Usher's syndrome and Infantile Refsum's disease. There are few effective clinical treatments for retinitis pigmentosa which affects an estimated 1.5 million individuals world-wide. However, understanding the histopathologic changes occurring in RP is critical to understanding the rationale for current therapies, as well as to develop future therapies. This book highlights the most recent research done in the field.