An information processing system is provided which determines whether a session in which an invited user has been invited to participate is still valid or not before participation in the session. The information processing system includes: storing status information indicating whether each of a plurality of sessions offering a service possibly participated in by the user is valid or not; and storing a plurality of items of invitation information about a plurality of invitations each being an invitation for the invited user to participate in one of the sessions. Each client device acquires one of the plurality of items of invitation information about the invitation for the user using the client device to become the invited user, and displays on a display screen the acquired item of invitation information in a manner reflecting the status information.