We use tree rings to investigate environmental impacts on tree growth and reconstruct past environmental changes. Our aim is to understand the underlying tree-physiological processes, particularly in relation to the water and carbon cycles. The spatio-temporal scale ranges from minutes to millennia and from cells to ecosystems around the globe. Our toolbox includes time series analysis of ring width, x-ray density, stable isotopes and wood cell anatomy. The analysis of tree rings is therefore a powerful approach for interdisciplinary research.