This DClinPsy thesis has been written in the format of three papers: a systematic review, an empirical paper and a critical reflection paper. Papers 1 and 2 will be submitted for publication in the journal entitled Research in Autism Spectrum Disorders. Paper 3 is not intended for submission. Paper one presents a systematic review investigating the relationship between Restrictive and Repetitive Behaviours (RRB) and anxiety symptoms. Paper two presents a quantitative study which explores the mediating role coping style has between autistic traits and symptoms of anxiety. Paper three presents a critical reflection on the process of conducting the research along with the methodological strengths and limitations contained in this thesis. The implications of the research for clinical practice and the relevance for clinical psychology are discussed.