Time-resolved optical techniques are used to explore electron spin dynamics in bulk and epilayer samples of n-type ZnO as a function of temperature and magnetic field. The bulk sample yields a spin coherence time T * 2 of 20 ns at T = 30 K. Epilayer samples, grown by pulsed laser deposition, show a maximum T * 2 of 2 ns at T = 10 K, with spin precession persisting up to T = 280 K.A lot of attention has been focused on zinc oxide (ZnO) because of material properties that make it well-suited for applications in ultra-violet light emitters, transparent high-power electronics and piezoelectric transducers. In addition, the theoretical work of Dietl et al ., 1 predicting room temperature ferromagnetism for Mn-doped p-type ZnO, has revealed the possibility that ZnO may be an appropriate candidate for spintronics. 2 The magnetic properties of thin films of ZnO with transition ion doping, 3,4,5 are being widely investigated, but practical spintronics applications would also require long spin coherence time and spin coherence length.