Universals of language have been studied extensively for the last four decades, allowing fundamental insight into the principles and general properties of human language. Only incidentally have researchers looked at the other end of the scale. And even when they did, they mostly just noted peculiar facts as ''quirks'' or ''unusual behavior'', without making too much of an effort at explaining them beyond calling them ''exceptions'' to various rules or generalizations. Rarissima and rara, features and properties found only in one or very few languages, tell us as much about the capacities and limits of human language(s) as do universals. Explaining the existence of such rare phenomena on the one hand, and the fact of their rareness or uniqueness on the other, is a reasonable and interesting challenge to any theory of how human language works. The present volume for the first time compiles selected papers on the study of rare linguistic features from various fields of linguistics and from a wide range of languages.