Descriptive grammarians and typologists often encounter unusual constructions or unfamiliar variants of otherwise familiar construction types. Many of these phenomena are puzzling from the perspective of linguistic theories: they neither predict these “anomalies” nor, arguably, provide the tools to describe them insightfully. This book analyzes an unusual type of relative clause found in many related and unrelated languages of Eurasia. While providing a detailed case study of Tundra Nenets, it broadens this inquiry into a detailed typological exploration of this relative clause type. The authors argue that an understanding of this construction requires exploring the (type of) grammar system in which it occurs in order to identify the (set of) independent constructions that motivate its existence. The resulting insights into grammar organization illustrate the usefulness of a construction-theoretic syntax and morphology informed by a developmental systems perspective for the understanding of complex grammatical phenomena.