Sleep remains enigmatic. Few scientists would contend that sleep is optional, yet no scientist could contend that the purpose of sleep is known. Given that disturbed sleep has probably been a hominin concern since long before the evolution of anatomically modern humans, it seems remarkable that so little has been discovered about sleep's primary purpose, and that progress has been so frustratingly slow in finding safe and effective ways to mitigate the problem. The present chapter discusses the very common but rarely specifically diagnosed or treated occurrence of sleep disturbances following a typical concussive brain injury (CBI). Many scholars have contributed to a recent acceleration in the characterization of the genetics and physiology of sleep, the classification and epidemiology of disorders of sleep, the understanding of multidimensional short- and long-term consequences of suboptimal sleep, and the effective management of sleep complaints. If one recent discovery stands out, it is that untreated sleep disorders are probably responsible for far more neurodegenerative morbidity and mortality than was previously appreciated. Sleep after concussion is its own subdiscipline within that larger research agenda -- and may exhibit unique features that perhaps require atypical interventions. Like the chapters on headache and fatigue, perhaps the most important practical significance of the present chapter is its discussion of management. Several recent observations and trials slightly encourage hope for eventual relief. The authors implore clinicians to investigate sleep in their post-concussive patients.