Birth defects are also referred to as \"congenital anomalies\" or \"congenital abnormalities\". This chapter gives Classification of congenital abnormalities. It focuses on various syndromes. It explains Neurofibromatosis syndrome, Marfan’s syndrome, Treacher Collins syndrome, Hypohidrotic ectodermal dysplasia syndrome, Turner’s syndrome, Klinefelter’s syndrome, Prader-Willi syndrome, William’s syndrome and Down’s syndrome.