PURPOSE: To explore the operationalization and measurement of sedentary behavior (SB) in individuals with cerebral palsy (CP). MATERIALS AND METHODS: We searched five databases from 2011 to 2020 for primary studies of experimental, qualitative, longitudinal, or observational designs measuring SB or postures typically characterized as sedentary (sitting, reclining, lying). RESULTS: We screened 1112 citations and selected 47 studies. SB was operationalized through muscle activation, energy expenditure or oxygen consumption in typically sedentary postures ( = 9), and through thresholds and postures used by accelerometers, activity monitors, and a questionnaire to measure time spent in SB ( = 25). Seven out of the eight studies that measured energy expenditure found ≤1.5 metabolic equivalents of task (METs) for sitting and lying. While different accelerometer thresholds were used to measure SB, the behavior (SB) was consistently operationalized as sitting and lying. Little consistency existed in the subpopulation, instruments and cut-points for studies on validity or reliability of tools for measuring SB ( = 19). CONCLUSIONS: Sitting and lying are considered sedentary postures, which is defined as ≤1.5 METs in individuals with CP. There is variability in the tools used to measure SB in individuals with CP. Therefore, consensus on the definition and reporting of SB is needed.Implications for rehabilitationAlthough sedentary behavior (SB) is increased in individuals with cerebral palsy (CP) compared to the typically developing population, there is no standard definition for SB for these individuals; this makes it difficult to synthesize data across studies.Sitting and lying are ≤1.5 METs in individuals with CP, suggesting we only need to measure posture to show change in SB.The commonly used accelerometer cut-point in the typically developing population of ≤100 counts per minute generally has excellent reliability across multiple devices in ambulatory children with CP.