Expenditure on plant and machinery has traditionally been seen as an indicator of future economic growth and productivity. But in the age of high technology, investment in an economy's knowledge base could be as important. Key areas include investment in research and development, in software and in human capital (measured by expenditure on higher education). Guy Woods presents data on these three indicators and a composite indicator, created by the OECD, which brings them together in to one indicator of investment in knowledge.