Titanosaurs are the only group of sauropodomorph dinosaurs that possesses osteoderms. The Anacleto and Allen formations (Upper Cretaceous) from northern Patagonia (Argentina) have provided an abundance of these elements, isolated or associated with more or less complete skeletons. Here, we study the morphology, microanatomy, and histology of titanosaur osteoderms found in these stratigraphic units. The size and gross anatomy of the osteoderms are strongly variable, as well as their microanatomy, which ranges from compact structures to those with strong development of cancellous bone. The primary bone tissue is composed of structural fiber bundles that are ossified by dermal metaplasia. Bone pathologies were identified in at least two osteoderms. Bone histology suggests that the osteoderms were entirely imbedded in the stratum compactum of the dermis. Titanosaur osteoderms were probably employed for multiple functions, including mineral storage and defense.