Abstract: Disclosed are various embodiments for geolocation- and time-based alerts that identify client devices that were in a specified geographic area at a specified time. A user of a client application may designate an alert that comprises a message, a specified geographic area or location, and a specified time. A computing environment that maintains geolocation data for various client devices may identify those client devices that were in the specified geographic area at the specified time and may communicate the alert to those client devices. A communication session may be established between a user who originated the alert and at least one other user of another client device.