The brittleness of Ir has become a challenging and puzzling problem for decades and its fundamental mechanisms are controversial with each other in the literature. The present first principles calculation aims to get a deep understanding of the brittleness of Ir from an elastic and electronic view. It is found that Ir has normal pressure-dependent mechanical behavior, while the temperature-dependent behavior of Ir is unusual and contrary to that of other FCC metals, and that pressure decreases the brittleness of Ir, whereas temperature increases its brittleness, suggesting that the machining of Ir products should be performed at low temperature and high pressure. Moreover, electronic structure and crystal field theory reveal that Ir has the mainly octahedral bonding, which would be transformed to the mainly cubic bonding under high pressure, while become more octahedral and directional at high temperature. In addition, the implication and importance of the similarities between Ir and semiconductors are also discussed. (C) 2012 Elsevier B.V. All rights reserved.