For decades, proteins have intrigued scientists with their dynamic nature and essential role in biological processes. Among them, prions stand out by defying the conventions of molecular biology, delving into the mystery of neurodegenerative diseases.My first contact with prions dates back to my DEA at the Université de Paris-Sud, where I was introduced to their fascinating world. This early fascination has guided me throughout my academic and professional career, leading me to explore in depth their role in conditions such as Alzheimer's and Creutzfeldt-Jakob disease. Today, as I write this book, I'm delving into the complex mysteries of prion proteins and their impact on brain health.