This chapter examines cognitive factors in sleep in children with autism spectrum disorder (ASD). Up to 80% of children with ASD have co-occurring sleep problems, and sleep disorders in children with ASD include insomnia, sleep-related breathing disorders, parasomnias, rapid eye movement associated abnormalities, rhythmic movement disorders, and restless legs syndrome. Sleep surveys, sleep diaries, actigraphy, and polysomnography may be used to evaluate sleep problems. Poor sleep affects cognition in adults and children without ASD as well as those with autism. Cognitive difficulties linked to poor sleep include tasks of executive functioning and overall academic performance. Effective intervention strategies include behavioral sleep education and the use of exogenous melatonin.