This chapter discusses properties of Ta (tantalum). Ta belongs to the group VB transition metals known for a strong tendency to solve interstitial impurities as H, O, N, C. The impurity problem could be overcome to a large extent by electron-beam zone melting combined with ultra-high vacuum degassing and purification techniques. Properties of Frenkel defects (FD), self-interstitial atoms (SIA), and vacancy (V) in tantalum are listed. The SIA-SA interaction and V-SA interaction data are also tabulated. Resistivity recovery of electron-irradiated tantalum at 5.5 K and 8 K is illustrated. High-purity foil samples prepared from UHV-zone refined material are used for the experiments. Influence of niobium, tungsten and zirconium doping on isochronal recovery curve and differential curve are illustrated. Crystallographic effects on single crystals for different irradiation energies are plotted. Resistivity recovery of neutron-irradiated tantalum, high-purity and oxygen-doped specimens are illustrated. The influence of oxygen and/or nitrogen on the resistivity recovery of tantalum following plastic deformation at room temperature is illustrated.