This dissertation introduces flow delegation, a novel concept to deal with flow table capacity bottlenecks in Software-defined Networks (SDNs). Such bottlenecks occur when SDN switches provide insufficient flow table capacity which can lead to performance degradation and/or network failures. Flow delegation addresses this well-known problem by automatically relocating flow rules from a bottlenecked switch to neighboring switches with spare capacity. Different from existing work, this new approach can be used on-demand in a transparent fashion, i.e., without changes to the network applications or other parts of the infrastructure. The thesis presents a system design and architecture capable of dealing with the numerous practical challenges associated with flow delegation, introduces suitable algorithms to efficiently mitigate bottlenecks taking future knowledge and multiple objectives into account and studies feasibility, performance, overhead, and scalability of the new approach covering different scenarios.