Limb and periscapular muscle weakness is the most common presentation of a person with a brachial plexopathy. Pain is a more variable symptom and is typically associated with trauma, neoplasm, and brachial neuritis. Postoperative plexopathies, rucksack-associated neuropathies, and radiation-induced neuropathies may present with minimal pain. In lower trunk injuries, patients may present with Horner syndrome. All evaluations should start with a thorough history followed by a complete neurological examination. Winging of the scapula may occur with brachial plexus lesions; the static and dynamic positions of the affected scapula may be associated with specific nerve lesions. The differential diagnosis of a patient presenting with upper limb pain and weakness is broad and includes other processes such as nerve root avulsions, radiculopathies, myelopathies, motor neuron disease, and peripheral nerve entrapments. This chapter discusses anatomy, classification, anatomic variants, and electrodiagnostic approach of branchial plexopathy.