  The advent of quantum devices, which exploit the two essential elements of
quantum physics, coherence and entanglement, has sparked renewed interest in
the control of open quantum systems. Successful implementations face the
challenge to preserve the relevant nonclassical features at the level of device
operation. A major obstacle is decoherence which is caused by interaction with
the environment. Optimal control theory is a tool that can be used to identify
control strategies in the presence of decoherence. We review here recent
advances in optimal control methodology that allow for tackling typical tasks
in device operation for open quantum systems and discuss examples of
relaxation-optimized dynamics. Optimal control theory is also a useful tool to
exploit the environment for control. We discuss examples and point out possible
future extensions.
