Theodosius II (Latin: Flavius Theodosius Junior Augustus; 10 April 401 – 28 July 450), commonly surnamed Theodosius the Younger, or Theodosius the Calligrapher, is Byzantine Emperor from 408 to 450.

He is mostly known for promulgating the Theodosian law code, and for the construction of the Theodosian Walls of Constantinople.

He also presides over the outbreak of two great Christological controversies, Nestorianism and Eutychianism.