Gmail’s filing system for email conversations is based around labels, which are more flexible and powerful than folders. With its original user interface, many users did not discover labels, and wondered why Gmail had no folders. The Gmail team redesigned the user interface for labeling to make it more discoverable and understandable, and to add the most useful functionality of folders. The new design works for the simple use case (a conversation with only one label), while still making the more complex use case (multiple labels) easily available. It has been launched to millions of users worldwide and has resulted in much higher adoption of labels, especially by new users of Gmail.