From the conceptual basis of the Effective Dose Equivalent, as introduced by ICRP into the dose limitation system, the procedure for calculating the relevant mean tissue dose equivalents is derived. The reference adult male and female phantoms are described briefly. Proposals are made for completing the definition for the Effective Dose Equivalent HE. Conversion functions between exposure in free air and organ doses as well as the Effective Dose Equivalent are given for external photon irradiation.