The aims of this thesis were threefold. First, an exploratory study of the Saudi mothers' stress, mental health status, ways of coping, social support provided to them and type of family structure preferred by them, which was achieved by recruiting twenty mothers of children with various Intellectual Disabilities (ID), (Study 1). Second, translating and modifying the original English measures, testing the psychometric properties and finding the new factors of the translated scales by recruiting sample of mothers with Typically Developing (TD) children (N=504) and mothers of ID children (N=513), (Studies 2 & 3). The first set of studies focused mainly on the development of measures that were translated into Arabic. The reliability and validity of all the measures were acceptable. Inserting tow additional religious coping items into the Brief COPE did not jeopardise the psychometric properties of the measures, but rather added to its predictive and construct validity. The third aim of this thesis, which was divided into two sub-studies (Chapters 9 and 10) focused on testing the hypothesised model of adjustment to ID by testing all mediating and moderating possibilities. Multiple regression modelling procedures permitted the identification of indirect and direct effects. Results revealed that mothers of children with ID showed higher levels of stress, anxiety and depression than mothers of TD children. In addition, Behavioural Disorders (BD) were significantly stronger than IQ in predicting maternal outcome and only some child and families characteristics have an effect on maternal well-being. Results also provided general support for the proposed model. Religious coping had a moderating effect between BD and maternal stress, between BD and maternal anxiety and between IQ and maternal anxiety. Emotion-focused coping showed a significant moderating effect on BD and maternal anxiety. Regarding social support, satisfaction with support (SPS) showed a nearly significant moderating effect between BD and maternal anxiety. The helpfulness of social support (FSS) showed a nearly significant effect between IQ and maternal stress. Whereas, network size (FSS2) had a significant moderating effect between IQ and maternal stress.