Researchers and developers are pursuing increasingly sophisticated roles for autonomous systems. Whether working within networked systems as software agents or embedded in robots and unmanned vehicles, what makes these systems valuable is their intelligent, active, and adaptive nature. These qualities are often characterized in intelligent systems literature by the word "autonomy"-a catch-all label that highlights the qualities of self-directedness and self-sufficiency in task performance. Though continuing research to make machines more active, adaptive, and functional is essential, the point of increasing such proficiencies is not merely to make the machines more independent during times when unsupervised activity is desirable or necessary, but also to make them more capable of sophisticated interdependent joint activity with people and other machines when such is required. That means autonomous systems must support not only fluid orchestration of task handoffs among different people and machines, but also combined participation on shared tasks requiring continuous and close interaction. HART research seeks to bring together the best thinking from diverse research communities in order to advance current and anticipated applications of intelligent human-machine collaboration, including the participation of humans as first-class citizens in collaboration with autonomous systems. This would enable autonomous systems not merely to do things for people, but also to work together with people and other systems-the inevitable next leap-forward required in autonomous system design and deployment.