This study uses high-resolution transmission electron microscopy (TEM) to investigate the atomic structure of reduced graphene oxide (RGO). The research reveals that RGO consists of defect-free graphene regions, interspersed with defective areas dominated by clustered pentagons and heptagons. These defective areas contain carbon atoms bonded to three neighbors in a planar sp² configuration, making them undetectable by spectroscopic techniques. The defective areas introduce significant in-plane distortions and strain in the surrounding lattice. The study shows that RGO is composed of intact graphene islands of sizes between 3 and 6 nm, interspersed with defect clusters forming planar, quasi-amorphous sp²-bonded areas. These findings align with the model proposed by Lerf and co-workers, but also reveal a significant amount of topological defects after reduction. The oxidation-reduction process leaves disordered carbon inclusions within the sheets, which are seamlessly connected to the crystalline areas. The graphene regions near these defects can be highly distorted, with in-plane and out-of-plane deformations observed. Isolated topological defects, mostly dislocations, are also present and may have formed as a result of strain. The effects of these defects must be considered in any comprehensive study of RGO's properties. Knowledge of the defect structures may help to devise procedures to remove them or lead to novel applications that take advantage of their presence. The study highlights the importance of understanding the atomic structure of RGO to fully exploit its properties.This study uses high-resolution transmission electron microscopy (TEM) to investigate the atomic structure of reduced graphene oxide (RGO). The research reveals that RGO consists of defect-free graphene regions, interspersed with defective areas dominated by clustered pentagons and heptagons. These defective areas contain carbon atoms bonded to three neighbors in a planar sp² configuration, making them undetectable by spectroscopic techniques. The defective areas introduce significant in-plane distortions and strain in the surrounding lattice. The study shows that RGO is composed of intact graphene islands of sizes between 3 and 6 nm, interspersed with defect clusters forming planar, quasi-amorphous sp²-bonded areas. These findings align with the model proposed by Lerf and co-workers, but also reveal a significant amount of topological defects after reduction. The oxidation-reduction process leaves disordered carbon inclusions within the sheets, which are seamlessly connected to the crystalline areas. The graphene regions near these defects can be highly distorted, with in-plane and out-of-plane deformations observed. Isolated topological defects, mostly dislocations, are also present and may have formed as a result of strain. The effects of these defects must be considered in any comprehensive study of RGO's properties. Knowledge of the defect structures may help to devise procedures to remove them or lead to novel applications that take advantage of their presence. The study highlights the importance of understanding the atomic structure of RGO to fully exploit its properties.