The present research investigated the use of a Smartphone App as an adjunct in the treatment of a range of anxiety disorders. The primary aim of the App was to increase client adherence to between session therapy tasks, involving homework practice of a range of skills and tasks known to be associated with successful treatment of anxiety disorders. Homework is an important component of many therapeutic approaches, allowing clients to practise therapeutic skills between sessions, as well as providing continuity between sessions (Freeman & Rosenfield, 2002). Greater client adherence to homework tasks has been associated with improved treatment outcomes, and may be particularly important for reducing the risk of relapse (Scheel, Hanson, & Razzhavaikina, 2004). However, despite the benefits of engagement with homework tasks, client adherence to these activities can often be a significant barrier to treatment (Addis & Jacobson, 2000; Burns & Nolenhoeksema, 1991; Detweiler & Whisman, 1999; Detweiler-Bedell & Whisman, 2005). It is also one area in which the use of adjunctive technologies may have the greatest impact. The aim of this paper was to describe the development and pilot testing of a therapeutic Smartphone application, namely, PsychAssist. This application was designed as an adjunct to face-to-face therapy in the treatment of anxiety disorders among adults. The App was developed with the purpose of enhancing client engagement and adherence to between session (homework) tasks to improve maintenance and generalization of therapeutic behaviours.