Forming heathy sleep-wake patterns in infancy can be beneficial not only for the infant themselves but parents as well. The development of sleep can be seen through both sleep-state organisation and sleep consolidation. This is vitally important as sleep plays an important role in brain development, as well as promoting health. Furthermore, when healthy sleep-wake patterns are not established in early infancy, the development of infant sleep problems may arise. Gradual behavioural interventions for infant sleep such as extinction with minimal check and extinction with parental presence, have shown to improve sleep behaviours through parental report. However, the nature of change is unknown, specifically do interventions change infant sleep behaviour or sleep-state architecture? Infants who do continue to require parental intervention and attention for sleep could in part be due to their temperament. Nine participants aged 12-18 months were recruited for this study, six of which had received a behavioural intervention for ISD and three which had not. VSG data was recorded during four phases, namely, baseline, intervention, post-intervention and follow-up. This data along with sleep diary data was analysed to answer the following questions; Firstly, was the gradual intervention effective in reducing ISD? Secondly, were changes shown in infant sleep behaviour or infant sleep architecture? And thirdly, was there any change in infant negative emotionality in relation to sleep changes? Results showed that a gradual behavioural intervention was effective in reducing infant ISD behaviours. Changes in sleep state architecture and sleep behaviours of infants were observed, as well as a change in negative emotionality of intervention infants. Therefore, this research provides some insight on how interventions effect the sleep of infants and how temperament may play a crucial role in ISD.