The QX200 Droplet Digital™ PCR (ddPCR™) System is used to partition a ddPCR reaction mixture into thousands of nanoliter-sized droplets. After each endpoint PCR on a thermal cycler, droplets are read individually as they are streamed single file past a two-color optical detection system on the QX200 Droplet Reader. The PCR-positive and PCR-negative droplets are counted to provide absolute quantification of target DNA. The system includes a QX200 Droplet Generator, QX200 Droplet Reader, and QuantaSoft™ software. The droplet generator and reader are CE-IVD marked for use in the European Union for in vitro diagnostics and are the only digital PCR instruments available for use in a clinical laboratory. Example applications include liquid biopsy cancer detection and monitoring, gene editing validation, viral load and residual disease monitoring, copy number determination, and gene expression analysis.