This study reorganizes the role of article similarity—operating as a precondition for assessing design similarity under the Design Protection Act—by separating it across distinct doctrinal contexts. Because a design is conceptually inseparable from its underlying article, the similarity of articles operates as an outcome-determinative variable not only at the application and registration stages, but throughout the entire enforcement of design rights. However, Korean case law has not sufficiently clarified the scope of articles that should serve as the basis for comparison in a particular context. This article first analyzes the U.S. Federal Circuit’s trilogy of decisions in Curver, Surgisil, and Columbia, examining the recent trend of aligning the scope of design patent protection, the scope of anticipatory prior art for novelty, and the scope of comparison prior art for infringement, all to the same article of manufacture identified in the claim. Next, it examines how Korean design protection practices determinethe scope of articles across five contexts: (i) prior art for assessing novelty, (ii) prior art for assessing non-obviousness, (iii) accused design in infringement analysis, (iv) prior art used to exclude known portions of a registered design when assessing the scope of protection, and (v) prior art invoked under the free-to-use design defense. The analysis shows that, in contexts (i), (iii), and (iv), Korean courts apply a uniform standard for article similarity, primarily based on the use and function of articles, with the common perception of consumers and traders taken into account as a complementary consideration. While substantive standards differ in detail, the U.S. Federal Circuit and Japanese courts likewise apply a single standard across these three contexts. However, Korea’s “interchangeability” theory—which finds article similarity whenever consumers could theoretically substitute heterogeneous articles for the same purpose—has at times been applied in an arbitrary manner, extending to situations that cannot reasonably be expected to occur in actual consumer behavior. To the extent that “interchangeability” is intended to serve the policy goal of using the novelty requirement to filter out designs that imitate those of heterogeneous articles, that goal is better pursued through the non-obviousness requirement rather than by expanding the scope of similar articles through a notion of interchangeability. Regarding contexts (ii) and (v), the practice of some lower courts requiring article similarity lacks a doctrinal foundation, and prior designs from adjacent product fields should be available for reference without such a restriction.