Stacking-fault energies in MoSi2, due to shear along (331), were calculated by means of ab initio and modified embedded-atom method calculations. The results were used to investigate the configurations of ½<331> dislocations and their mobility. Shear of 1/6<331> on the {103} plane of MoSi2 produced an antiphase boundary whose geometry was different to that produced by 1/6<331> shear in the opposite direction. Modified embedded-atom method calculations showed that the first type of dislocation configuration was stable, while both types of calculation showed that the second type of dislocation configuration was unstable. Both ab initio and modified embedded-atom method calculations showed that there was a stable fault close to the second type of dislocation configuration, with a displacement of about 1/8<331> in the same direction. The calculations also showed that there was a stable fault in the <110> plane with a displacement of 1/4<111>. The identical fault was produced by a shear of ¼<331> There was good agreement between the fault energies calculated using the two methods, and also with the experimental value (200 to 370mJ/m2). The agreement between the calculated fault energies in the <013> plane was not so good. One factor was that the relaxation procedures were different; the modified embedded-atom method had more flexibility and involved a larger number of atoms; perhaps explaining why it gave lower stable fault energies. The <103> planes had an unusual five-layer ABCDE stacking sequence, with successive planes off-set by 1/5<301>. Shear of 1/10<351> in the correct direction gave a low-energy fault with Mo atoms surrounded by the correct number (10) of Si nearest-neighbours. This vector was close to the 1/8<331> shear that produced a stable fault and might explain its low calculated energy. Various dissociated configurations of ½<331> dislocations were considered on the basis of 1/6<331>, 1/8<331>, ¼<331> and 1/10<351> partials. All could have asymmetrical arrangements which responded differently to the direction of the applied stress; thus explaining why {103}<331> slip was much easier for crystals compressed along [100] than along [001]. Stacking-Fault Energy and Yield Stress Asymmetry in Molybdenum Disilicide. T.E.Mitchell, M.I.Baskes, S.P.Chen, J.P.Hirth, R.G.Hoagland: Philosophical Magazine A, 2001, 81[5], 1079-97