Principal Purpose Test restricts treaty benefits where obtaining benefit was a principal purpose, subject to object and purpose exception. The guidance explains that the Principal Purpose Test permits denial of treaty benefits where, on an objective assessment of all relevant facts, obtaining the benefit was one of the principal purposes of an arrangement, unless it is established that granting the benefit accords with the object and purpose of the relevant treaty provision; it instructs that the PPT is to be applied prospectively, specifies interaction rules for bilateral incorporations and MLI incorporation timing, and excludes certain treaty-specific grandfathering provisions from the PPT while endorsing a context-specific, fact-based assessment with reference to BEPS Action 6 and the UN Model Commentary as supplementary guidance.