Pattern library

A pattern library is a documented collection of recurring UI patterns — search results, empty states, multi-step forms, data tables — with guidance on when and how to use each one. It's narrower than a design system (which also covers tokens, foundations and governance) and broader than a component library (which is just the coded parts).

Pattern libraries pre-date the term "design system" by about a decade — Yahoo Pattern Library in 2006 is the canonical example — and the concept survived because patterns answer questions components can't: not "what does a button look like" but "what does a successful checkout flow look like". Most mature design systems include a patterns section for exactly this reason.

Related: Design system · Component library · Atomic design · Style guide