The paper reviews the pathophysiology of both acute and chronic peripheral nerve entrapments. Factors influencing susceptibility of the nerve fibers to such an injury were presented. Pathophysiological mechanisms influencing extent of the injury of the nerve were looked at, taking into consideration cases of double crush syndrome. Moreover, pathological changes occuring in the instances of short-lasting acute compression of the nerve were described, namely metabolic conduction block and segmental, local perinodal demyelinisation with partial or complete conduction block. Furthermore, microscopic and ultrastructural changes found in chronically compressed nerves were presented in detail, explaining the mechanisms of demyelinisation injury in the early phase of entrapment neuropathy and demyelinisation-axonal injury in the advanced stage of the disease. This paper reviews two best known grading systems of peripheral nerve injuries i.e. Seddon’s and Sunderland’s classifications which assess the functional condition of the nerve and ongoing histological changes. These classifications were explained along with neurophysiological data in order to facilitate understanding of neurography and EMG tests results as the guide for therapy and prognosis.