Because developmental activity-dependent synaptic plasticity has been hypothesized to participate in network refinement, leading to the precise mapping of synaptic contacts constituting a functional brain, it is important to investigate the spatio-temporal structure of immature network activities. This article is briefly reviewing 15 years of studies on the immature rat hippocampus which, together with recent results obtained from awake rat pups, represent an important step toward the understanding of spontaneous patterns of activity and their potential implication in network maturation. Due to synergistic excitatory actions of GABA and glutamate receptor mediated signals during early postnatal life, spontaneous patterns of hippocampal activity that have been characterized both in vitro and in vivo are likely to provide hebbian modulation of developing glutamatergic and GABAergic synapses. Together with studies on trophic actions of these transmitters, study of the immature hippocampal network patterns and plasticities allows for multiple technical and conceptual approaches and represents an interesting experimental model for development studies.