The international landscape of vocational education and training (VET) is hugely diverse – and more diverse than most other sectors of education systems. There is wide variation across countries in how vocational programmes are organised and delivered, the ages and stages of education at which individuals pursue VET and how VET is funded. This diversity creates an opportunity to exploit cross-country variation to identify the features of VET systems associated with better educational, labour market and social outcomes for graduates. At the same time, country comparisons need good data, but comparative data on VET have major gaps. This report identifies existing and new indicators of VET systems that are suitable for international comparisons, based on current data availability and quality. The report does not directly fill those data gaps, but establishes the dimensions of the gaps and sets out how one might go about filling them, while giving some proposals for future indicator development.