Metagenomics is becoming more widely used for diagnosis of viral infections and surveillance of viruses. Its pathogen-agnostic approach makes metagenomics useful for unknown and novel infection diagnosis, outbreak investigation, and new and emerging pathogen surveillance. New metagenomics methods, such as the use of rapid sequencing technologies and approaches that can selectively enrich for a wide range of viruses, are expanding the range of clinical and public health scenarios in which metagenomics can be used. Following the COVID-19 pandemic, there is increasing interest in viral surveillance worldwide, using clinical samples, potential zoonotic reservoirs and environmental sources, such as wastewater. Validation and accreditation of metagenomics protocols to ensure quality, together with further innovation in methods, will be necessary to bring metagenomics into routine service in clinical and public health laboratories.