This thesis explores different aspects of parents’ perceptions of Autism Spectrum Disorder (ASD) across three individual papers. The first paper presents a systematic review focusing on parents’ beliefs about the cause and course of their child’s autism. The review synthesises the results of fifteen studies which met the inclusion criteria to update the findings of a previous review. Parents held a range of etiological beliefs, although genetics/heritability, pre and post natal exposure, brain abnormalities and religious beliefs were the most common. Culture and socio-demographic variables were associated with parents’ beliefs and influenced their perceptions about the course of ASD along with a number of personal and healthcare decisions. Methodological constraints and variation in reporting results presented difficulties in comparing these findings to the previous research and providing an accurate conclusion regarding the most widely accepted belief. Areas for future research are highlighted along with clinical recommendations for improved parent-professional communication and the provision of evidence-based information to facilitate informed decision-making. The second paper presents the results from an empirical study which looked at parents’ lived experience of the ASD assessment process when a diagnosis was not given. Parents’ views in this context have previously been underrepresented. In total six interviews were conducted and parents’ experiences were explored using interpretative phenomenological analysis. Three superordinate themes transpired which illustrated the issues that parents encountered in recognising, disclosing and celebrating their child’s differences, the emotional and psychological impact of the assessment, along with difficulties in understanding the outcome. Research limitations and clinical implications are discussed. The final paper considers the clinical and theoretical implications arising from both papers. Recommendations for best practice include more professional training, pre and post assessment counselling, needs-led service provision, policy development and ongoing audit and evaluation. A personal reflection of the research process is provided.