In a knowledge-based economy, business performance and overall levels of economic growth are increasingly dependent on the development and exploitation of intellectual assets. A number of OECD countries offer tax incentives to encourage and reward business expenditures on intellectual assets. This working paper examines the tax treatment of corporate expenditures on selected intellectual assets and develops an indicator of the relative generosity of tax systems in OECD countries to such investments. Five types of intellectual assets are considered: research and development (R&D), patents, workforce training, software and organisational change. The paper shows that although tax incentives have, to date, mainly favoured R&D expenditures, they are gradually embracing other types of intellectual assets, especially in those countries that provide more generous tax treatment of R&D. Nineteen OECD countries had specific R&D tax incentives in place in 2005, up from only 12 in 1996, and 6 offered tax incentives for corporate training.