Inherited ataxias and hereditary spastic paraplegias are two heterogeneous groups of neurodegenerative disorders with a wide spectrum of clinical symptoms and also, with a remarkable number of involved loci/genes. Inherited ataxias are clinically characterized by progressive degeneration of cerebellum and spinocerebellar tracts of the spinal cord associated with a variable combination of signs of central and peripheral nervous system. Hereditary spastic paraplegias (HSPs) are characterized by slowly progressive spasticity and weakness of lower limbs, due to pyramidal tract dysfunction. The classification of these diseases is extremely difficult because of overlapping symptoms among different clinical forms. For this reason, the genetic classification for both inherited ataxias and HSP forms, based on the causative loci/genes has reached general acceptance. The aim of this review is to summarize the genetics and the pathogenic mechanisms involved in these two groups of neurodegenerative spinocerebellar disorders.