  Device concepts in semiconductor spintronics make long spin lifetimes
desirable, and the requirements put on spin control by schemes of quantum
information processing are even more demanding. Unfortunately, due to
spin-orbit coupling electron spins in semiconductors are generically subject to
rather fast decoherence. In two-dimensional quantum wells made of zinc-blende
semiconductors, however, the spin-orbit interaction can be engineered in such a
way that persistent spin structures with extraordinarily long spin lifetimes
arise even in the presence of disorder and imperfections. We review
experimental and theoretical developments on this subject both for $n$-doped
and $p$-doped structures, and we discuss possible device applications.
