Delivering real-time services (Internet telephony, video conferencing, and streaming media as well as business-critical data applications) across the Internet requires end-to-end quality of service (QoS) guarantees, which requires a hierarchy of contracts. These standardized contracts may be referred to as Service Level Agreements (SLAs). SLAs provide a mechanism for service providers and customers to flexibly specify the service to be delivered. The emergence of bandwidth and service agents, traders, brokers, exchanges and contracts can provide an institutional and business framework to support effective competition. This article identifies issues that must be addressed by SLAs for consumer applications. We introduce a simple taxonomy for classifying SLAs based on the identity of the contracting parties. We conclude by discussing implications for public policy, Internet architecture, and competition.