This book is concerned with our current understanding of natural climate change, its variability on decadal to centennial time-scales, the extent to which climate models of different kinds simulate past variability, and the role of past climate variability in explaining changes to natural ecosystems and to human society over the later part of the Holocene. It highlights the need to improve not only our understanding of the physical system through time but also to improve our knowledge of how people may have influenced the climate system in the past and have been influenced by it, both directly and indirectly