This study estimates the impacts of several business investment tax breaks (including tax credits and instant write offs) implemented over the past 15 years in Australia. The paper exploits exogenous changes in qualifying thresholds to identify the impact of these policies on both the intensive and extensive margins. While the policies implemented during the GFC had a material effect on investment, there is more limited evidence of an effect for other policies, including those implemented during COVID-19. The study finds more evidence of an effect when focusing on unincorporated businesses, who do not utilise the dividend imputation, consistent with the ‘old view’ of corporate finance. Taken together these results suggest these policies may only be effective in limited circumstances.