Objective: The effectiveness of self-help materials may be constrained by failures to undertake recommended exercises or to deploy the techniques that one has learned at the critical moment. The present randomized controlled trial investigated whether augmenting self-help materials with if-then plans (or implementation intentions) could overcome these problems and enhance the self-management of anxiety symptoms. Method: At baseline, participants who reported anxiety symptoms completed the Hospital Anxiety and Depression Scale (HADS) and the state version of the State-Trait Anxiety Inventory (STAI). Participants were then randomized via a computer program to standard self-help (n = 86), augmented self-help (n = 90), or no-intervention (n = 86) conditions. Eight weeks later, 95% (n = 249) of the participants completed the HADS and STAI again. Results: Findings showed a significant reduction in anxiety in the augmented self-help condition compared with both the standard self-help and no-intervention conditions (caseness rates on the HADS at follow-up were 21%, 49%, and 44%, respectively). Mediation analyses indicated that the benefits of augmented self-help materials were explained by improved detection of anxiety-related triggers and greater experienced benefits of the self-help techniques. Conclusions: These findings suggest that implementation intentions offer a valuable supplement to self-help materials that can enhance their impact on outcomes. (Contains 3 footnotes, 3 tables, and 1 figure.)