The electronic structure of LiFePO4 underpins transport properties important to its use as a lithium storage electrode. Here we have calculated the electronic structure of LiFePO4 in the ordered olivine structure by a first-principles method to determine (i) the effective mass of carriers and (ii) the nature of the band structure. The electrical conductivity in high purity undoped LiFePO4 has also been measured experimentally. Spin-polarized calculations show a large electron effective mass and a much smaller but highly anisotropic hole effective mass, suggesting that hole-doped compositions should have the greater electronic conductivity. More surprisingly, the calculations show that this polyanion compound is a half-metal with spin-sensitive band structure, like some other oxides being studied for spintronics applications. This previously unappreciated aspect of the LiFePO4 electronic structure may play a role in determining transport properties including those relevant to electrochemical applications. (C) 2004 The Electrochemical Society.