In the context of the proposed European CCCTB there is clearly a perceived need for the introduction of a common thin capitalization rule. This rule would be aimed at dealing with inbound investment emerging from both third countries, and from Member States opting out of the CCCTB. The principal aim of this paper is to establish whether such a need does indeed exist, and if so, which considerations should guide the design of a thin capitalization rule for the CCCTB. The paper starts by provid...