Simulation studies highlight the potential of COVID-19 contact tracing apps in controlling the SARS-CoV-2 pandemic. However, tracing apps have to be adopted by a large proportion of the population in order to make a substantial contribution to “flatten the curve”. App quality characteristics such as engagement, functionality, aesthetics, and information might be important for acceptance and adoption in the population. User acceptance might be especially of importance in situation where app usage is voluntary and not mandatory i.e. by legal regulations. The project aims to systematically review app quality characteristics of COVID-19 contact tracing apps. The study will be restricted to member states of the European Union, former members (United Kingdom) and countries of the European Free Trade Association as these countries seem to have comparable legal standards of information-security and voluntariness of app usage. Associations between quality characteristics, national adoption rates and COVID-19-infection and -death rates will be explored. As a result, the project seeks to find quality aspects for COVID-19 contact tracing apps which may contribute to higher rates of adoption and to provide an overview of best practice features within the apps rated to inspire further app development.