Disclosed herein are technologies that allow users to create, issue, accept and participate in gaming challenges. A gaming challenge involves participants playing a gaming application to improve their rank on a leaderboard associated with the application until challenge conditions are met or the challenge expires. Challenges can be time-based, objective-based, a tournament or of other type. A challengor can create a challenge by specifying a gaming application to be played, the leaderboard to be used in the challenge, challenge type, challenge duration, and additional challenge criteria. A gaming service can maintain the leaderboard and pass challenge-related notifications between participants. Participants' computing devices can send notices indicating when a challenge has been met or when a participant's relative ranking has changed. A challengor or challengee can select an avatar expression for animating an avatar when a challenge request or acceptance or decline of a challenge is presented at a computing device.