The aim of the current thesis was to conduct experimental analyses of the emotional impact of cognitive defusion techniques on positive and negative thoughts about the self. Part I of the thesis investigated the impact of defusion on explicit self-report measures. Experiment 1 examined the emotional impact of a brief defusion technique on positive and negative self-statements. In this case, defusion was manipulated through the use of pro- or anti-defusion instructions and prefixing the statements with defused or non-defused phrases (e.g. “I am having the thought that I am a bad person”). The results indicated that the defusion-related instructions had little or no impact on the explicit ratings, but the defusion prefix decreased statement discomfort while increasing statement believability and willingness. Indeed, this effect occurred only for negative statements, but positive statements remained unchanged on all measures. In Experiment 2, participants’ personalised self-statements were targeted for more direct intervention that involved defusion, thought control or placebo. In each case, the impact of instructions versus exercise was also assessed. In these findings, there was some superiority of defusion exercise over instructions, although defusion was generally associated again with decreased discomfort. However, willingness did not change and the believability of the statements now decreased. Thought Control overall decreased discomfort but had no impact on believability or willingness. No changes were associated with Placebo. Part II of the current thesis attempted to examine the utility of defusion in the context of both explicit and implicit measures. Experiments 3 through 6 employed the Implicit Relational Assessment Procedure (IRAP) to determine the most suitable types of self-relevant stimuli that could be targeted by the implicit measure while being susceptible to a defusion intervention. Participants’ responses to positive and negative words were compared in the context of I AM versus I AM NOT (Experiment 3); I AM versus OTHERS ARE (Experiment 4); and I AM versus I SHOULD BE (Experiment 5). The results indicated strong positive implicit self-regard across all three contexts, although I AM versus I SHOULD BE showed the weakest levels of implicit positive self-regard, relative to the other two experiments. Experiment 6 replaced the target words with whole statements (e.g. ‘I am so alone that it hurts’) to determine if this would be associated with lower levels of implicit self-regard and indeed it was. Experiment 7 provided a preliminary exploration of the susceptibility of the Statement-IRAP to defusion with groups of individuals with different levels of experience with defusion. Undergraduates (with no experience with defusion) were compared with a group of therapists (with considerable defusion experience). Although both groups reported strong implicit positive self-regard, those with more defusion experience were associated with stronger implicit outcomes. Experiment 8 investigated the impact of a defusion intervention or Placebo on implicit self-regard in individuals with no prior history of defusion. The data indicated that defusion increased implicit positive self-regard more than Placebo. The results presented here offer one of the first comprehensive experimental analyses of the impact of defusion on both explicit and implicit measures. Overall, the findings highlight the positive emotional benefits of defusion, relative to other more traditional coping strategies.