This chapter focuses on the basic principles of computed tomography (CT) and magnetic resonance imaging (MRI) used for imaging the brain structure. Indications for brain imaging in Behavioral Neurology & Neuropsychiatry (BN&NP) patients include: poison or toxin exposures, dementia or cognitive decline of unknown etiology, delirium, brain injuries of any type with ongoing symptoms, new-onset psychiatric symptoms, abnormal neurological findings suggesting brain pathology, and new-onset atypical psychosis. Imaging of the brain with MRI depends on the polar characteristics of the water molecule and its unique behavior within a strong magnetic field. Factors important to consider when choosing an imaging modality include type of suspected pathology, acuity of the illness, and desired planes of section. Doppler ultrasound (US) evaluation has been used successfully in clinical neurology as a screening tool to evaluate internal carotid artery (ICA) disease.