OBJECTIVE: To systematically review the literature regarding rest and return to activity after sport-related concussion. DATA SOURCES: The search was conducted in the Cochrane Central Register of Controlled Trials, CINAHL, SPORTDiscus, Educational Resources Information Center, Ovid MEDLINE, and PubMed using terms related to concussion, mild traumatic brain injury, physical and cognitive rest, and return to activity. STUDY SELECTION: Studies were included if they were published in English; were original research; and evaluated the use of, compliance with, or effectiveness of physical or cognitive rest or provided empirical evidence supporting the graded return-to-activity progression. DATA EXTRACTION: The study design, patient or participant sample, interventions used, outcome measures, main results, and conclusions were extracted, as appropriate, from each article. DATA SYNTHESIS: Articles were categorized into groups based on their ability to address one of the primary clinical questions of interest: use of rest, rest effectiveness, compliance with recommendations, or outcome after graded return-to-activity progression. A qualitative synthesis of the results was provided, along with summary tables. CONCLUSIONS: Our main findings suggest that rest is underused by health care providers, recommendations for rest are broad and not specific to individual patients, an initial period of moderate physical and cognitive rest (eg, limited physical activity and light mental activity) may improve outcomes during the acute postinjury phase, significant variability in the use of assessment tools and compliance with recommended return-to-activity guidelines exists, and additional research is needed to empirically evaluate the effectiveness of graded return-to-activity progressions. Furthermore, there is a significant need to translate knowledge of best practices in concussion management to primary care providers.