This thesis examines the importance of taxation on firm investment. The thesis shows that low tax rates are effective at increasing investment in an international context, but also that the design of tax system can cause significant distortions in the incentives for firms to invest. The first chapter of this thesis shows the significance of the complete tax system, outside of simple corporate statutory tax rates, on determining foreign investment inflows. The second chapter shows how government intervention in the credit market can have positive or adverse effects on the investment and risk-taking of small businesses. The final chapter looks at how the corporate tax system's treatment of corporate losses affects the incentive for firms to invest based on their profitability. The thesis provides new understanding of the importance of tax design in affecting firm investment behaviour.