With the idea of operating the factors affecting the mobility or the pinning of ferroelectric domain walls in AB03 perovskites, high resolution electron microscopy has been performed to provide a better knowledge of the walls themselves in PbTiO/sub 3/. The transition between two domains with their polarisation vectors at right angles appears to be along the (101) twin planes. The Maxwell equations can be satisfied by a highly localized space charge rather than a lattice distortion. As the heavy atom Pb lattice seems not to be distorted, light atoms, such as Ti or O, must create charge. Highly accurate calculations are also required to observe the variations due to small changes in the positions of the light atoms.