Despite the reliance of cooperative applications on the facilities provided by distributed systems, little consideration is given by these systems to the support of cooperative work. This paper examines the provision of appropriate mechanisms to represent cooperative work within a distributed platform. Based upon a examination of existing models of cooperative activity and the experiences of their use, a lightweight model of activities is suggested as the basis for the supporting platform. Rather than concentrate on the exchange of information, this lightweight model focus on the mechanisms of sharing of objects. This focus enables a clear separation between the mechanisms provided by the distributed platform and the policy which is the responsibility of the cooperative applications.