This book contains a selection of chapters aimed to provide a better understanding prion structure and biology. Together these chapters provide an overview of prion biology and underscore some of the challenges we face if we want to understand how this lively pathogen propagates and evolves in mammals. There is also mounting evidence that studying prion biology has a wider relevance due to similarities in the processes of protein misfolding and aggregation between prion disorders and other neurodegenerative disorders such as Alzheimer?s, Parkinson?s, and Huntington?s diseases.