Abstract: Results obtained by atomic computer simulation based on an adapted Stillinger–Weber (SW) potential concerning the structure and relative stability of lattice dislocations, tilt and twin boundaries in GaN are discussed. The method used for the search and description of all possible atomic configurations depends on the crystallographic structure; consequently it is of general application and the results are transferable to the wurtzite binary compounds. On the contrary, the relaxed structures and their relative energetic stability are potential dependent. The results presented here correspond to a GaN model described by a pair potential. Whenever it has been possible our results have been compared with experiments or with ab initio calculations. We present the core shape and energy of a and c crystal dislocations of both edge and screw character; [0001] tilt boundaries of misorientation angles from 9.3° (corresponding to Σ37) to θ = 44.8° (corresponding to Σ43) and (10-1n) twin boundaries (n = 1, 2, 3) [1, 2, 3, 4]. The atomic structures of the tilt boundaries can be described in terms of the three stable structures of the prism a-edge dislocation core. The (10-13) twin boundary is entirely described by 6-coordinated channels whereas the other twin boundaries present more complex structural units.