The peripheral nervous system is that part of the nervous system outside the brain and spinal cord. The peripheral nervous system is often described with the muscle, and indeed neuropathologists deliver diagnosis on both nerve and muscle pathology other than on pathology of the central nervous system. The peripheral nervous system includes the cranial nerves and spinal nerves. In this chapter, we will present on the development of the epimeric and hypomeric muscle, myogenic and neurogenic myopathies, as well as the non-neoplastic and neoplastic of the peripheral nervous system. Motor neuron dysfunction results in hypotonia or paralysis. Sensory neuron dysfunction results in abnormal or lost sensation. Some of the disorders, particularly the mitochondrial myopathies, are often progressive and fatal. Illustrative materials for schwannoma, neurofibroma, and malignant peripheral nerve sheath tumor are provided.