This report presents the youth Digital Skills Indicator (yDSI), a unique, extensively crossnationally validated measurement tool with 31 items, distributed over digital skills and digital knowledge questions, that can be used for large-scale population research. The yDSI is the only measurement tool for youth digital skills that has been tested using the full range of validation practices. Over a period of six months, consultation with experts (face validity), cognitive interviews (content validity), pilot surveys (construct validity) and performance tests (criterion validity) with young people were conducted in a wide range of European countries. A review of the literature led to a framework identifying four dimensions that constitute digital skills: (1) technical and operational skills; (2) information navigation and processing skills; (3) communication and interaction skills; and (4) content creation and production skills.