Neurodegenerative diseases are a heterogeneous group of age-related disorders characterised by the progressive degeneration or death of neurons in the central or peripheral nervous system. The prevalence of these diseases is increasing, in part due to an ageing population, and the economic burden on healthcare systems is growing as a result. Genetic factors are key players in the pathogenesis of several neurodegenerative diseases, acting both as monogenic causes in inherited forms and as modulating factors in multifactorial/sporadic forms. Recent advances in low-cost genetic analysis have greatly advanced our knowledge of the genetic basis of several neurodegenerative diseases, improving our understanding of the mechanisms underlying their pathogenesis. In the era of precision medicine, a better characterisation of genotype-phenotype correlations can improve therapeutic approaches, help to assess individual drug responses, and help to guide gene-targeted clinical trials. This Special Issue provides an overview of research into the genotypes and phenotypes of neurodegenerative diseases, ranging from the use of cutting-edge omics techniques to the identification of biomarkers and the characterisation of new experimental models. The picture that emerges is one of ongoing research efforts to more effectively combat these devastating diseases and to identify potential future therapeutic targets.