Rare disease, also called Orphen disease, is any disease that affects a small percentage of the population. According to WHO, rare disease refers to disease that affects 0.65‰to 1‰ of the population. The huge amount of rare disease victims have not been given enough attention in China: we lack basic data on rare diseases and high diagnosis error rate is characteristic of rare disease cases. This is the first monograph to systemically decribe rare diseases and will be constructive for the recognition, diagnosis and treatment of rare diseases in China.