Cross-border intra-group debt represents a significant proportion of total global monetary flows. Responding to tax base erosion from related party interest deductions, countries have introduced domestic rules against “interest stripping” but the heterogeneity of these rules leads to double taxation and double non-taxation. The OECD’s 2013 Base Erosion and Profit Shifting (BEPS) Action Plan endorsed by the G20 identifies debt deductions as “Action Item 4”, for reform by the end of 2015. This article surveys the existing approaches, from “stand-alone” to “worldwide ratio” rules. The author concludes that the worldwide approach is preferable, and recommends that more countries adopt such a rule, limiting the local leverage ratio to the third-party leverage ratio of the worldwide group. Such a rule is principled, given the fungibility and other unique features of finance, can draw upon existing rules in three countries and achieves the BEPS project aim of eliminating a large capacity for profit shifting.