In enterprise networks, all aspects of the network, such as placement of security devices and performance, must be carefully considered. Even with forethought, networks operators are ultimately unaware of intra-subnet traffic. The inability to monitor intra-subnet traffic leads to blind spots in the network where compromised hosts have unfettered access to the network for spreading and reconnaissance. While network security middleboxes help to address compromises, they are limited in only seeing a subset of all network traffic that traverses routed infrastructure, which is where middleboxes are frequently deployed. Furthermore, traditional middleboxes are inherently limited to network-level information when making security decisions. Software-defined networking (SDN) is a networking paradigm that allows logically centralized control of network switches and routers. SDN can help address visibility concerns while providing the benefits of a centralized network control platform, but traditional switch-based SDN leads to concerns of scalability and is ultimately limited in that only network-level information is available to the controller. This dissertation addresses these SDN limitations in the enterprise by pushing the SDN functionality to the end-hosts. In doing so, we address scalability concerns and provide network operators with better situational awareness by incorporating system-level and graphical user interface (GUI) context into network information handled by the controller. By incorporating host-context, our approach shows a modest 16% reduction in flows that can be processed each second compared to switch-based SDN. In comparison to enterprise networks, residential networks are much more constrained. Residential networks are limited in that the operators typically lack the experience necessary to properly secure the network. As a result, devices on home networks are sometimes compromised and, unbeknownst to the home user, perform nefarious acts such as distributed denial of services (DDoS) attacks on the Internet. Even with operator expertise in residential networks, the network infrastructure is limited to a resource-constrained router that is not extensible. Fortunately, SDN has the potential to increase security and network control in residential networks by outsourcing functionality to the cloud where third-party experts can provide proper support. In residential networks, this dissertation uses SDN along with cloud-based resources to introduce enterprise-grade network security solutions where previously infeasible. As part of our residential efforts, we build and evaluate device-agnostic security solutions that are able to better protect the increasing number of Internet of Things (IoT) devices. Our work also shows that the performance of outsourcing residential network control to the cloud is feasible for up to 90% of home networks in the United States.