The Earth's surface is perpetually being displaced due to temporally varying atmospheric, oceanic and continental water mass distribution that loads the surface. These load-induced signals contribute significantly to the scatter in geodetic observations of particularly vertical displacements. We will outline the primary principles involved in modelling the surface displacements and gravity changes induced by surface mass loading including the basic theory, the Earth model and the surface load data. We then identify a list of issues, that need to be addressed when applying predicted load-induced displacements in time series analyses. A detailed analyses of the uncertainties in the computation of the predictions, reveals that the uncertainties in the surface load model constitutes the main limitation for the accuracy of the predictions.