Material design icons are the official icon set from Google that are designed under the material design guidelines.
Read the developer guide on how to use the material design icons in your project.
In css-sprite and svg-sprite are pre-generated sprite sheets. Instructions for using them are in the sprites documentation.
If you wish to use the icon set with Polymer, we recommend consuming them via the <iron-icons> element (<core-icons> in v0.5).
We have made these icons available for you to incorporate them into your products under the Creative Common Attribution 4.0 International License (CC-BY 4.0). Feel free to remix and re-share these icons and documentation in your products. We'd love attribution in your app's about screen, but it's not required. The only thing we ask is that you not re-sell the icons themselves.