Behavioural problems exhibited by children with Intellectual and Developmental Disabilities (IDD) have been identified as a significant stressor for family members in both cross-sectional and longitudinal research. However, the extent to which family members are affected by child behavioural problems is variable which may be due to moderating factors between these relationships, including resilience. There is a lack of conceptual clarity in defining what resilience is in existing research, and it is unclear how resilience may improve well-being outcomes in this population. This thesis presented four studies. One study investigated mothers’ reporting on their child’s resilience where it was found that maternal depression had a significant effect on child behavioural and emotional problems. The study found that child resilience functioned as a compensatory factor, being associated with fewer child behavioural problems. Three studies investigated resilience and related constructs in mothers of children with IDD. Social support was found to function as a protective factor between child behavioural problems and maternal depression, life satisfaction and when mothers reported the positive affect of having a child with IDD on themselves and their family. There was also some evidence of the role of practical coping and positive perceptions acting as protective factors between child behavioural and emotional problems and maternal well-being. Consistent evidence was found that maternal resilience functioned as a compensatory factor, improving maternal outcomes; including stress, anxiety, depression, perceptions of positive gain and family satisfaction. One study focused only on mothers of children with Autism Spectrum Disorder (ASD) where the severity of the child’s current ASD symptoms was found to have a significant main effect on maternal depression. Longitudinally maternal resilience did not act as a significant predictor of maternal well-being outcomes over time. Finally, findings from the empirical studies were discussed along with their implications for future research and interventions.