Digital technologies are being harnessed to support the public-health response to COVID-19 worldwide, including population surveillance, case identification, contact tracing and evaluation of interventions on the basis of mobility data and communication with the public. These rapid responses leverage billions of mobile phones, large online datasets, connected devices, relatively low-cost computing resources and advances in machine learning and natural language processing. This Review aims to capture the breadth of digital innovations for the public-health response to COVID-19 worldwide and their limitations, and barriers to their implementation, including legal, ethical and privacy barriers, as well as organizational and workforce barriers. The future of public health is likely to become increasingly digital, and we review the need for the alignment of international strategies for the regulation, evaluation and use of digital technologies to strengthen pandemic management, and future preparedness for COVID-19 and other infectious diseases. Public-health need Digital tool or technology Example of use Refs. Digital epidemiological surveillance Machine learning Web-based epidemic intelligence tools and online syndromic surveillance Web-based epidemic intelligence tools: 20-23,25 Based on social media or online search data: 30-33 Survey apps and websites Symptom reporting 37,38,48,49 Data extraction and visualization Data dashboard 39-45 Rapid case identification Connected diagnostic device Point-of-care diagnosis 58 Sensors including wearables Febrile symptoms checking 51-53 Machine learning Medical image analysis 65,66