Traditionally, both national and firm accounting practices treated investment in non-market intangibles, such as internal R&D, as current expenditure rather than as investment. National accounts have now started to capitalise, even if only partially, investments in intangibles such as software and R&D. However, most intangible investment is still excluded from the national accounts. In particular, the rate of change of output per worker increases more rapidly in the presence of intangible capital, and capital deepening -tangible and intangible - becomes the dominant source of labour productivity growth.