  The paper reviews the interplay of Rashba/Dresselhaus spin splittings in
various two dimensional systems made of III-V, wurtzite and SiGe. We discuss
the symmetry aspects of the linear and cubic in electron wavevector spin
splitting in heterostructures prepared on (001)-, (110)-, (111)-, (113)-,
(112)-, and (013)-oriented substrates and address the requirements for
suppression of spin relaxation and realization of the persistent spin helix
state. In experimental part of the paper we overview experimental results on
the interplay of Rashba/Dresselhaus spin splittings probed by photogalvanic
spectroscopy: the method based on the phenomenological equivalence of the
linear-in-wavevector spin splitting and several photogalvanic phenomena.
