Clinical neurophysiology (CNP) is a time-honored medical specialty that continues to make great strides, bolstered by rapid advances in neuroscience, biomedical engineering, and computer technology. It encompasses a wide range of methods and techniques for recording, presenting, and analyzing neurophysiologic signals in order to diagnose sensory, motor, autonomic, and central nervous system disorders. Testing performed in CNP or procedures used in current neurological practice include a variety of modality-specific and mixed-modality tests. Modality-specific CNP tests are performed to assess specific functional modalities using biomedical instruments that measure changes in neurophysiologic signals that occur spontaneously or with activation. Mixed-modality CNP tests utilize two or more test modalities to assess complex states (e.g., sleep, coma), to track multiple physiologic parameters, or to obtain more accurate results. CNP tests are classified based on functional anatomy or neural pathway tested. This chapter discusses artifact recognition and presents sources of artifacts in clinical neurophysiologic testing.