Neurodegenerative diseases share the common property of neuronal loss in the higher-order association and limbic cortices or the extrapyramidal and pyramidal motor systems. In addition, oligodendroglia, astrocytes, and microglia have been implicated in fundamental abnormalities of virtually every neurodegenerative disorder. The particular system affected, more importantly the distribution of the pathology, determines the clinical presentation. While the most common dementia and movement disorders, such as Alzheimer’s disease, Lewy body disease, and frontotemporal lobar degeneration with TDP-43 pathology, including amyotrophic lateral sclerosis, have been extensively studied, many less common, even rare neurodegenerative disorders have gained more attention in recent years. This shift in focus is perhaps driven, in part, by the severely underestimated financial costs associated with these diseases, as well as the immense emotional burden they impose on patients and their caregivers. This book presents the most recent developments in rare neurodegenerative disorders. Insights gained from the investigation of pathophysiological mechanisms of these rare disorders may lead to the development of therapeutic strategies for more prevalent neurodegenerative disorders. In addition to highlighting advancements in research, the book discusses the significant challenges faced by researchers and healthcare professionals in diagnosing and treating rare diseases. It emphasizes the critical need for continued funding and support for research, which is essential to improving patient outcomes and advancing our understanding of these complex conditions.