This dissertation aimed to explore the bases of security provided by the therapeutic relationship for clients with anxiety, considered from the perspective of Bowlby’s attachment theory. Empirical findings were presented to demonstrate the associations between insecure attachment patterns and the development of anxiety disorders in children and adults. Studies investigating the therapeutic relationship as a type of attachment with reference to clients with anxiety were outlined. Two case studies of psychotherapy (CBT and psychodynamic therapy) with anxious clients were examined to describe how the therapeutic relationship was of value and provided a secure base to the client. In both types of treatment, a strong therapeutic relationship facilitated the assessment of the client’s Internal Working Models and contributed to the success of the interventions. Transference was found to exist in both the CBT and the psychodynamic case. In the CBT case analysis and resolution of negative transference enhanced this type of treatment. The usefulness of attachment theory to psychotherapy and areas for future research were discussed.