Genetic Programming Theory and Practice VI was developed from the sixth workshop at the University of Michigan's Center? For the Study of Complex Systems to facilitate the exchange of ideas and information related to the thriving field of Genetic Programming (GP). The text explores the synergy between theory and practice, producing a comprehensive view of the state of the art in GP applications. This contribution addresses some significant interdependent themes that emerged from this year's workshop, including:? (1) Creating an efficient and effective use of test data.