Autism Spectrum Disorder (ASD) is classified as a neurodevelopmental disability and a relatively common diagnosis. It is marked by communication difficulties, social interaction problems and repeating behaviours. Many children with ASD have trouble sleeping such as taking longer time to fall asleep or sleeping less. Researchers have studied melatonin a hormone produced by the pineal gland from serotonin and tryptophan as a possible way to improve these sleep problems. Melatonin levels naturally rise in the evening and fall in the morning however children with ASD often have lower levels which can worsen their sleep difficulties. This thesis looked into whether melatonin helps children with ASD sleep better over both the short and long term and also examined its safety. It also addressed whether non-drug methods like cognitive behavioural therapy (CBT) could enhance melatonin effects. A search in PubMed using the keywords "melatonin sleep in children with autism", "Randomized Controlled Trial Melatonin Autism" and "melatonin in children sleep ASD" found five randomised controlled trials (RCTs). The studies showed that melatonin helped children with ASD fall asleep faster, longer and less wake up during the night. When melatonin was combined with strategies such as CBT the results were even stronger. Overall children who took melatonin tolerated it well and their sleep improved suggesting that melatonin may be a valuable treatment for addressing sleep issues in children with ASD.