Circles is a core feature of the Google+ Social Platform. It enables users to organize people into groups or lists for sharing across various Google products and services. Organization of circles is done through a drag-and-drop interface. Once a circle is created, a Google+ user can share specific private content to only that circle. For example, work themed content can be shared with only colleagues, and one's friends and family could see more personal content and photos. The option to share Public or with Everyone is always available. Users were originally able to create Shared Circles, a one-time share to promote a circle of individuals, but the feature has been removed.
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 (click on) 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.