»Interpolation as an Ability-to-Pay-Compliant Refrain from Taxation. An Analysis of the Interpolation of Tax Exemption Provisions in Real Estate Transfer Tax Law«: Interpolation is a method developed by the Federal Tax Court to apply tax exemptions of the Real Estate Transfer Tax Act beyond their wording. The work raises the question of a methodologically and systematically viable reasoning for this. Based on the justification of the real estate transfer tax against the constitutional background of the ability-to-pay principle, the work develops its own approach to interpolation, for which the tax exemptions are categorized according to their function.