This paper introduces the notion of profile-based cooperation as a way to support awareness and informal communication between mobile users during chance encounters. We describe the design of Proem, a wearable system for profile-based cooperation that enables users to publish and exchange personal profile information during physical encounters. The Proem system is used to initiate contact between individuals by identifying mutual interests or common friends. In contrast to most previous research that concentrates on collaboration in well-defined and closed user groups, Proem supports informal communication between individuals who have never met before and who don’t know each other. We illustrate the benefits of profile-based cooperation by describing several usage scenarios for the Proem system.