Polymer is an open-source JavaScript library for building web applications using Web Components. The library is being developed by Google developers and contributors on GitHub. Modern design principles are implemented as a separate project using Google's Material Design design principles.

Polymer is used by a number of Google services and websites, including the redesigned YouTube, YouTube Gaming, the redesigned Google Earth, Google I/O websites, Google Play Music, redesign of Google Sites and Allo for web.

Other notable users include Netflix, Electronics Arts, Comcast, Nuxeo, ING, Coca-Cola, McDonald's, BBVA, IBM and General Electric.