Sensors in Medicine 2021 seeks to highlight the most innovative advances in biosensor applications in medicine and healthcare. SiM21, the 9th in this annual series and the 2nd in virtual space, is not the largest conference on biosensors but arguably is the most important because it deals specifically with innovative applications in medicine and healthcare. Established biosensor applications in pregnancy testing and diabetes monitoring are now joined by infectious disease, cancer and other diagnostic tests. New Point of Care tests, Linear Flow platforms, Wearable and Implantable biosensors now appear almost daily.