Cabinet Decision No. 39 of 2019, Article 53, mandates the 'arm's length principle' for all transactions between linked entities. This means pricing must mirror what would be applied between two independent parties. Entities must use reasonably available information to evaluate these prices at the time of the transaction or, at the latest, by the tax return filing deadline for that period. This principle is fundamental to preventing tax base erosion by ensuring that related-party pricing is not artificially manipulated to reduce the overall taxable income in Qatar.