Recent modelling studies have shown that timely isolation of contacts can be effective in reducing the COVID-19 reproduction rate. The epidemiological features of COVID-19 put it in the region where contact tracing is a viable public health strategy but it needs to occur at exceptional speed to control transmission. This need for speed has led policymakers to consider adopting contact tracing apps that enable rapid digital contact tracing. The rapidity and perfect scalability of digital contact tracing make it superior to manual contact tracing for an infection such as COVID-19. However, digital contact tracing has to enable notification of contacts the instant a user becomes positive. Ideally, with a rapid follow-up call by public health officials. A number of contact tracing apps currently deployed – such as the Australian COVIDSafe app – do not allow instantaneous notification and are therefore very limited in their ability to achieve control. Digital tracing apps also require sufficient uptake to realise the benefits. This requires building and maintaining strong social licence for use by demonstrating that the benefits to the user are high and that privacy and security risks are low. Like many medical devices and therapies, contact tracing apps are “credence goods”, and claims of efficacy and safety must be largely taken on trust. Therefore Governments ought to subject these apps to robust and transparent evaluation so that users can judge for themselves whether downloading and use are worth the effort. This paper is intended for policymakers and provides an introduction to how digital contact tracing works, including a simplified model of its epidemiological foundations, and explores how to obtain enhanced uptake by achieving social licence for the use of the technology within the context of a public health emergency.