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We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

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It has been realized for a long time that knowing the η and η ′ wave functions in terms of quark and gluon components probes our understanding of nonperturbative QCD dynamics. Great effort has been given to this challenge, yet no clear picture has emerged even with the most recent KLOE data. We point out which measurements would be most helpful in arriving at a more definite conclusion. A better knowledge of these wave functions will significantly help to disentangle the weight of different decay subprocesses in semileptonic decays of D + , D + s and B + mesons. The resulting insights will be instrumental in treating even nonleptonic B transitions involving η and η ′ and their CP asymmetries; thus they can sharpen the case for or against new physics intervening there.