This paper considers the proposals of the Mirrlees Review to introduce an allowance for corporate equity (ACE) in the corporation tax system. It assesses how an ACE would affect various dimensions of corporate decision making. Broadly, the ACE would introduce neutrality in decisions as to the scale of investment and the source of finance. But it would leave distortions in choices regarding many mutually exclusive discrete choices, such as location and profit shifting. The paper presents some evidence on the likely impact of introducing an ACE, which depends on how the government makes up for foregone corporation tax revenue. It also considers briefly more radical options such as a destination-based corporate tax.