Palaeontological data plays a key role in reconstructing the biology, ecology, and evolution of the biosphere throughout the history of Life on Earth. Whereas modern molecular-based technologies have led to significant progress in understanding the developmental biology and phylogenetic relationships of extant animal phyla, Cambrian soft-bodied fossils represent the only way of studying the morphology of their extinct ancestors. This chapter provides an overview of the significance of exceptionally preserved Cambrian fossils and their contribution towards illuminating the origin of animal body plans. Over the last few decades, conceptual and technical advances have distanced Cambrian fossils away from their previous misconception as failed evolutionary experiments. Current efforts focus instead on clarifying the evolutionary links between these fascinating organisms and their extant descendants, made possible in part by the discovery of new exceptional deposits, and the improved knowledge of their unusual geological history capable of preserving delicate but informative tissues such as guts and brains.