Spin coherence has been studied in self-assembled (In,Ga)As/GaAs quantum dots which contain on average a single electron per dot due to n-type modulation doping. A magnetic field was applied in the Voigt geometry, in order to study the precession of the electron spins which are oriented normal to the field. Here we address the mechanism by which such a normal orientation can be achieved by resonant excitation with circularly polarized laser pulses. Further, we discuss, how long this coherence is maintained within an ensemble of quantum dots. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.