This open access book describes Smittestopp, the first Norwegian system for digital contact tracing of Covid-19 infections, which was developed in March and early April 2020. The system was deployed after five weeks of development and was active for a little more than two months, when a drop in infection levels in Norway and privacy concerns led to shutting it down.  The intention of this book is twofold.  First, it reports on the design choices made in the development phase.  Second, as one of the only systems in the world that collected population data into a central...