In this thesis, ferroelastic domain switching behaviour of lead zirconate titanate ceramics, as used in devices such as actuators, was studied. In particular, the effect of cyclic frequency and amplitude were assessed to develop a correlation between macrostructural changes and fatigue behaviour, both in the bulk and in crack-tip process zones. A variety of experimental methods were used. Raman scattering enabled the poling state of the ceramics can be determined. However, it could not distinguish between the different preferred orientations of in-plane c-domains. Conversely, neutron and X-ray diffraction technique can detect domain orientation distribution and the preferred direction of c-domains. In this study, neutron diffraction was used to probe domain switching behaviour in bulk samples while high spatial resolution X-rays were employed to analyse a switching zone near a crack tip. Under cyclic mechanical loading, domain switching and the accumulation of ferroelastic strain becomes saturated with increasing number of cycles. Moreover, time-dependent deformation was investigated. The results show that a domain forward-switching process occurs during creep deformation while a domain backward-switching process takes place during recovery. In addition, it was found that the frequency of applied stress affects the saturation of the ferroelastic strain while its magnitude has an influence on the level of strain accumulated. Under static mechanical loading, it was found that the size of the crack-tip zone where stress-induced domain switching occurs with increase in the stress intensity factor but the degree of domain switching around the crack tip changes only slightly. Under cyclic electrical loading, the results present a strong link between the frequency of the applied field, remnant polarisation, domain switching and the resultant crack growth. The results show that polarisation fatigue, the size of the switching zone, and the crack growth rate is greater at lower loading frequency. The quantitative analysis of the time dependent mechanism as well as the effect of loading frequency and amplitude on domain switching was achieved by applying viscoelastic models. Importantly, these models can be used to explain domain switching behaviour and domain wall movement under cyclic loading and link these processes to macroscopic deformation.