Across the expanding literature on the sense of agency, the striking reports of inserted thoughts from patients seeking psychiatric help are widely characterised as misattributions of agency for thought. However, this characterisation has recently been challenged, and key questions remain about both the phenomenology and etiology of these experiences. In this thesis, I draw a novel distinction between two distinct strands in the sense of agency for thought, ·and call on this distinction to develop a phenomenological analysis of these delusions of thought insertion, as well as another symptom of schizophrenia commonly characterised in terms of an anomalous experience of agency - auditory verbal hallucination (AVH). I point out fundamental problems with the leading etiologial model of abnormalities to the sense of agency for thought - the motor control-based comparator account - and develop a new and substantially revised version of this account. Finally, I investigate misattributions of agency for thought in the general population, presenting two novel experimental paradigms that make the source of thought ambiguous and allow measurement of the frequency, timing and --henomenology of misattributed thoughts. Across three studies, the prevalence of misattribution in a 5 minute trial was 72%,47% and 75%, respectively, suggesting that, in certain circumstances, the experience of agency for thought is not robust, and that ordinary episodes of thought will be readily misattributed to another agent. Results indicated that an arousing negative or positive thought is more likely to be misattributed than a neutral control. The results also showed that proneness to delusional beliefs - but not to auditory hallucination - was associated with greater frequency of misattributions. Overall, the results raise the possibility that thought insertion - and potentially other thought interference delusions - may be explained by appeal to general abnormalities in reasoning and belief formation, without any appeal to deficits in the sense of agency.