Models of the glacial isostatic adjustment (GIA) process, which is dominated by the influence of the Late Pleistocene cycle of glaciation and deglaciation, require two fundamental inputs: a history of ice-sheet loading and a model of the radial variation of mantle viscosity. These models may be tested and refined by comparing relative sea-level history predictions to geological inferences of such histories based upon appropriate sea level indicators from the same regions. Such comparisons are crucial in the development of models of the internal structure of the Earth’s mantle and in the determination of models of Late Quaternary continental glaciation history, but they also play a crucial role in our understanding of climate change-induced sea-level rise. In this short presentation, I will present an overview of our knowledge of the glacial isostatic adjustment phenomenon and how we can use it to learn more about the Earth's rheology, while putting this work in the context of anthropogenically induced global change and sea-level rise.