This policy brief discusses the role of testing for COVID 19 as part of any plan to lift confinement restrictions and prepare for a possible new wave of viral infections. If all confinement restrictions are lifted before a vaccine or effective treatments are developed without other measures to suppress new infections, the infection rate is expected to rebound rapidly. Crucially, quick suppression of infections requires testing more people to identify who is infected; tracking them to make sure they do not spread the disease further; and tracing with whom they have been in contact. This brief discusses how testing strategies can be used to achieve three main goals: 1) suppressing the resurgence of local outbreaks; 2) identifying people who have developed some form of immunity and can safely return to work; and 3) gaining intelligence on the evolution of the epidemic, including on when a threshold for herd immunity has been reached. The brief discusses what tests can be used for each goal, as well as practical implementation issues with testing strategies, including the opportunities and risks of using digital tools in this context.