PrefLib: a library for preferences. We introduce PrefLib: A library for preferences; an online resource located at “”. With the emergence of computational social choice and an increased awareness of the applicability of preference reasoning techniques to areas ranging from recommendation systems to kidney exchanges, the interest in preferences has never been higher. We hope to encourage the growth of all facets of preference reasoning by establishing a centralized repository of high quality data based around simple, delimited data formats. We detail the challenges of constructing such a repository, provide a survey of the initial release of the library, and invite the community to use and help expand PrefLib.