Peripheral nerves are complex organs that can be found throughout the body reaching almost all tissues and organs to provide motor and/or sensory innervation. A parenchyma (the noble component made by the nerve fibers, i.e., axons and Schwann cells) and a stroma (the scaffold made of various connective elements) can be recognized. Although morphological analysis is the most common approach for studying peripheral nerve regeneration, researchers are not always aware of several histological peculiarities of these organs. Therefore, the aim of this review is to describe, at a structural and ultrastructural level, the main features of the parenchyma and the stroma of the normal undamaged nerve as well as the most important morphological changes that occur after nerve damage and during posttraumatic nerve regeneration. The paper is aimed at providing the reader with the basic framework information on nerve morphology. This would enable the correct interpretation of morphological data obtained by many experimental studies on peripheral nerve repair and regeneration such as those outlined in several other papers included in this special issue of the International Review of Neurobiology.