  It is control that turns scientific knowledge into useful technology: in
physics and engineering it provides a systematic way for driving a system from
a given initial state into a desired target state with minimized expenditure of
energy and resources -- as famously applied in the Apollo programme. As one of
the cornerstones for enabling quantum technologies, optimal quantum control
keeps evolving and expanding into areas as diverse as quantum-enhanced sensing,
manipulation of single spins, photons, or atoms, optical spectroscopy,
photochemistry, magnetic resonance (spectroscopy as well as medical imaging),
quantum information processing and quantum simulation. --- Here
state-of-the-art quantum control techniques are reviewed and put into
perspective by a consortium uniting expertise in optimal control theory and
applications to spectroscopy, imaging, quantum dynamics of closed and open
systems. We address key challenges and sketch a roadmap to future developments.
