Ocular misalignment and nystagmus result in the visual symptoms of binocular diplopia and oscillopsia, and are frequently encountered in neurological practice. Correct localization of the underlying problem is the first step to accurate diagnosis, and requires a systematic approach and knowledge of the ocular motor pathways and actions of the extraocular muscles. This article contains three segments: The first outlines the diagnostic approach with attention to fine historical and examination details helpful in localization; the second describes common localizations of diplopia including extraocular muscle, neuromuscular junction, cranial nerve and nuclei, and supranuclear structures with attention to examination features characteristic for each location; and the third describes the types of acquired nystagmus and their treatments.