Google+ Circles allow Google+ users to organize people into groups for sharing across various Google products and services. Although other users are able to view a list of people in a user's collection of Circles, they cannot view the names of those Circles. The privacy settings also allow users to hide the users in their Circles as well as who has them in their Circle. Organization is done through a drag-and-drop interface. This system replaces the typical friends list function used by sites such as Facebook. After adding a user to a Circle, it isn't until they are notified and have drag-and-dropped the other user to one of their circles that they are mutually in each others' Circles.
Another function of Circles is to control the content of one's Stream. A user may click on a Circle on the left side of the page and the Stream portion of the page (the center) will contain only posts shared by users in that Circle. For the unsegmented Stream (includes content from all of a user's Circles), each Circle has a "slider" configuration item with four positions: nothing, some things, most things, and everything. The nothing position requires the user to select the Circle name explicitly to see content from users in that Circle. The everything setting, as its name implies, filters nothing out from people in that Circle. The remaining two positions control the quantity of posts which appear in one's main Stream, but the algorithm controlling what shows has not been disclosed. The default Circles are Friends, Family, Acquaintances, and Following. These circles names can be changed, and the Following circle is always at the top of the "Add to circle" list when on a Google+ Page. The Following Circle is described as "People you don't know personally, but whose posts you find interesting."
- It is currently not possible to post to both a Circle and a community (except by creating two posts). The same way, it is not possible to post to two communities at once.
- Circle sharing is static, not dynamic. Which means that it won't be updated if the creator of the Circle Share post adds or removes people afterward; a Circle Share is a "snapshot" at a given moment. This behaviour is intentional. Both statif Shared Circles and Dynamic Shared Circles would make sense for different reasons, but Google only allows the former.