Actigraphy is a method used to study sleep-wake patterns and circadian rhythms by assessing movement, most commonly of the wrist. These evidence-based practice parameters are an update to the Practice Parameters for the Use of Actigraphy in the Clinical Assessment of Sleep Disorders, published in 1995. These practice parameters were developed by the Standards of Practice Committee and reviewed and approved by the Board of Directors of the American Academy of Sleep Medicine. Recommendations are based on the accompanying comprehensive review of the medical literature regarding the role of actigraphy, which was developed by a task force commissioned by the American Academy of Sleep Medicine. The following recommendations serve as a guide to the appropriate use of actigraphy. Actigraphy is reliable and valid for detecting sleep in normal, healthy populations, but less reliable for detecting disturbed sleep. Although actigraphy is not indicated for the routine diagnosis, assessment, or management of any of the sleep disorders, it may serve as a useful adjunct to routine clinical evaluation of insomnia, circadian-rhythm disorders, and excessive sleepiness, and may be helpful in the assessment of specific aspects of some disorders, such as insomnia and restless legs syndrome/periodic limb movement disorder. The assessment of daytime sleepiness, the demonstration of multiday human-rest activity patterns, and the estimation of sleep-wake patterns are potential uses of actigraphy in clinical situations where other techniques cannot provide similar information (e.g., psychiatric ward patients). Superiority of actigraphy placement on different parts of the body is not currently established. Actigraphy may be useful in characterizing and monitoring circadian rhythm patterns or disturbances in certain special populations (e.g., children, demented individuals), and appears useful as an outcome measure in certain applications and populations. Although actigraphy may be a useful adjunct to portable sleep apnea testing, the use of actigraphy alone in the detection of sleep apnea is not currently established. Specific technical recommendations are discussed, such as using concomitant completion of a sleep log for artifact rejection and timing of lights out and on; conducting actigraphy studies for a minimum of three consecutive 24-hour periods; requiring raw data inspection; permitting some preprocessing of movement counts; stating that epoch lengths up to 1 minute are usually sufficient, except for circadian rhythm assessment; requiring interpretation to be performed manually by visual inspection; and allowing automatic scoring in addition to manual scoring methods.