The intelligent use of tools is a general and important human competence that AI research has not yet examined in depth. Other fields have studied the topic, however, with results we can compile into a broad characterization of habile (tool-using) agents. In this paper we give an overview of research on the use of physical tools, using this information to motivate the development of artificial habile agents. Specifically, we describe how research goals and methods in animal cognition overlap with those in artificial intelligence. We argue that analysis of activities of tool-using agents offers an informative way to evaluate intelligence.