  Structured output feedback controller synthesis is an exciting recent concept
in modern control design, which bridges between theory and practice in so far
as it allows for the first time to apply sophisticated mathematical design
paradigms like $H_\infty$- or $H_2$-control within control architectures
preferred by practitioners. The new approach to structured $H_\infty$-control,
developed by the authors during the past decade, is rooted in a change of
paradigm in the synthesis algorithms. Structured design is no longer be based
on solving algebraic Riccati equations or matrix inequalities. Instead,
optimization-based design techniques are required. In this essay we indicate
why structured controller synthesis is central in modern control engineering.
We explain why non-smooth optimization techniques are needed to compute
structured control laws, and we point to software tools which enable
practitioners to use these new tools in high technology applications.
