Intrinsic charge disorder inherent to the lead-based relaxor ferroelectrics crucially influences the structure of these materials at all length scales. Interfaces that are formed due to the charge disorder are so-called low-angle domain walls, the unique dynamics of which contributes to strongly nonlinear and hysteretic responses to external stimuli, affecting the global behaviour of relaxor ferroelectrics. Focus of the lecture will be on the link between the local and mesoscale structure of PMN-PT ceramics across compositions and their dielectric and piezoelectric properties.