Quality-of-Service routing satisfies performance requirements of applications and maximizes utilization of network resources by selecting paths based on the resource needs of application sessions and link load. QoS routing can significantly increase the number of reserved bandwidth sessions that a network can carry, while meeting application QoS requirements. Most research on QoS routing to date, has focused on routing within a single domain. BGP, the de facto standard for inter-domain routing provides no support for QoS routing, and has well-documented performance related issues that lead to its inadequacy to support QoS. This paper proposes new approaches to inter-domain routing for sessions requiring guaranteed QoS. The performance-scalability tradeoff is explored via extensive experiments on the proposed algorithms. Our extensive experiments on realistic intra-domain ISP topologies as well as inter-domain settings, show that the proposed algorithms achieve at least an order of magnitude gain in performance (blocking probability) over current mechanisms, while remaining scalable and easy to deploy.