This article describes the development of a mobile app that provides cognitive and behavioural strategies to help people change their gambling behaviour, called Change for Better (C4B). This mobile-based intervention was adapted from a cognitive behavioural therapy (CBT) app for substance use disorders. The C4B app includes many core components of CBT. Currently, the app is being evaluated in a randomized control trial to determine its use and effectiveness as an adjunct therapy for adults seeking treatment for gambling disorder.