evidence: Viruses accumulate mutations in their genomes as they spread from person to person. By comparing the genomes of different SARS-CoV-2 samples collected at different times in different places, and by combining these data with contact tracing data, it is possible to establish the genealogy and mutation rate of SARS-CoV-2, and thereby trace its origin and when and where it spread. Current data indicates that SARS-CoV-2 made its jump from animals to humans sometime during Fall 2019 and had already spread outside of China by January 2020.