Our changing climate will affect human lives in manifold ways. Especially sea-level rise is driven by diminishing amounts of snow and land ice. The cryosphere as part of the Earth’s climate system provides interconnecting feedbacks between its components, leading to multifaceted changes. To understand these feedback mechanisms we have to consider the various interactions between the atmosphere, the oceans and the ice covering both polar land and seas. The state and evolution of Earth’s glaciers and ice sheets play a key role therein and thus profound ice physics knowledge with respect to ice sheet dynamics is required. Ice sheet dynamics on multiple scales, from microscopic processes to continental-sized phenomena, are in the focus of scientific attention to improve climate predictions on a global scale. The state and evolution of ice sheets and glaciers is partly recorded in deep ice cores drilled through the Antarctic and Greenlandic ice. Advanced analysis of ice core material can teach us the climate history of our planet and reveal physical mechanisms leading to ice motion. The mapping of ice micro-structures, which are reflecting the deformation and recrystallisation processes that control ice sheet flow reveal the active processes in the material. The connection between ice dynamics, microstructures, process modelling as well as phenomenological modelling of ice deformation then tests and completes our current understanding of ice sheet dynamics and result in improved future projections.