Service Level Agreements (SLAs) are currently one of the major research topics in Grid Computing, as they serve as a foundation for reliable and predictable Grids. SLAs define an explicit statement of expectations and obligations in a business relationship between provider and customer. Thus, SLAs should guarantee the desired and a-priori negotiated Quality of Service (QoS), which is a mandatory prerequisite for the Next Generation Grids. The complexity of an SLA-based workflow grows significantly, as characteristics of correlated sub-jobs, the data transfer phases, the deadline constraints and possible failures have to be considered. Thus, an architect for an SLA-aware workflow implementation needs sophisticated mechanisms for specification and management, sub-job mapping, data transfer optimization and fault reaction. Therefore, this book presents a system for SLA-aware Grid workflows. The main contributions include an improved specification language for SLA-aware workflows, three mapping and optimization algorithms for sub-job assignment to Grid resources, an error recovery mechanism, and a prototype imple-mentation using standard middleware.