Neurodegenerative diseases are complex, progressive disorders in which molecular pathology, neuronal dysfunction, and neuropsychiatric manifestations interact across the disease course. Recent advances in Alzheimer's disease, Parkinson's disease, and related disorders increasingly connect mechanistic discoveries with biomarkers, improved phenotyping, and emerging therapeutic strategies. Nevertheless, substantial gaps remain, including heterogeneous diagnostic and symptom-assessment frameworks, limited mechanistic specificity, and comparatively sparse evidence for non-Alzheimer neurodegenerative disorders. This Special Issue, New Insights into Neurodegenerative Diseases, aims to integrate basic, translational, and clinical perspectives addressing disease mechanisms, neuroinflammation, neuropsychiatric manifestations, biomarker development, diagnosis, therapeutic innovation, and precision medicine. Particular attention is given to studies that bridge laboratory discoveries with clinically meaningful phenotypes and interventions, promote multidimensional approaches to disease characterization, and identify new directions for earlier detection, individualized treatment, and improved patient outcomes.