This chapter talks about the AlxFe1-x alloy. The long range ordering B2 phase of AlFe alloy has been investigated in detail because of its possible technical applications at high temperatures. A further characteristic of this alloy is (like for some other B2 alloys) the ability to retain large quantities of vacancies. These vacancies are considered as “quenched” thermal vacancies and not as constitutional equilibrium vacancies. The defect annealing has been investigated by measurements of the electrical resistivity after e--irradiation and neutron irradiation. From PAS investigation, after quenching of AlFe3 and some mixed phases vacancy migration energies are given. The annealing after quenching is summarized in figures. Annealing after cold work is shown. The concentrations of thermal vacancies and their dependencies on stoichiometry are shown; there seem to be no dramatic changes as a function of stoichiometry. From PAS investigation, after quenching of AlFe3 and some mixed phases vacancy migration energies are given. Differential isochronal recovery spectrum of a cold worked Al0.40Fe0.60 ordered alloy and vacancy concentrations as determined by DD for different temperatures and alloy compositions is illustrated. Isochronal annealing of the electrical resistivity for Al0.40Fe0.60 single crystals after e--irradiation and fast neutron irradiation at 21 K with beam direction is shown. Isochronal recovery of the change of the electrical resistivity as observed after quenching of Al0.40Fe0.60 ordered alloys from different temperatures are provided.