The difficulty that humans have in perceiving and understanding large scale phenomena is widely acknowledged. The need to study and understand processes associated with global environmental change has created an environment that has promoted unprecedented scientific co-operation between and within disciplines. The science of global change emphasises the need to understand the complex biophysical systems both in terms of components and as a whole. This has involved research at many levels of organisation, or scales, within each system. The need to link and integrate information between scales underlies the scientific approaches described in this book. The theory, practice and challenges of scaling are discussed using examples from current research, combining biology and geography to address issues at a range of scales, from local to global levels.