The protection of a third party who relies on the officially registered status of immovable property lies at the heart of conflicts between registered rights and prior unregistered claims. Iran’s Law on Mandatory Official Registration of Immovable Property Transactions and the implementing regulation of Article 10 expressly introduce the concept of a bona fide third party into Iranian land-registration law. Yet the legal function of good faith, its relationship with official registration, the relevant standard of knowledge, the proper time for assessment, the burden of proof, and the consequences of bad faith remain insufficiently differentiated. Using an analytical and functional comparative method, this article distinguishes four separate dimensions: the constitutive effect of registration, opposability, the public faith of the land register, and the protection of third-party reliance. It then draws limited analytical lessons from German and French law before examining Articles 10 and 35 of the Iranian framework. The analysis shows that good faith is neither a general condition for the creation of ownership nor synonymous with possession of an official title. Rather, it functions as an additional condition for protecting an officially registered position against a prior unregistered claim. The statutory language of lack of awareness and actual knowledge supports an actual-knowledge starting point and does not, without further legal basis, establish an autonomous “knew or ought to have known” standard. Objective circumstances may nevertheless serve as evidence of actual knowledge. Finally, proof of bad faith does not automatically invalidate the official title: its consequences must be distinguished among loss of protective status, liability for current value, and the separately conditioned possibility of recovery of the property itself.