Oscillations within and across neuronal systems are believed to serve various complex functions, such as perception, cognition, movement initiation, plasticity and memory. GABAergic interneurons and their inhibitory synapses play a major role in these oscillatory patterns. Networks of inhibitory interneurons impose a coordinated oscillatory "context" for the "content" carried by networks of principal cells. This hypothesis implies that GABAergic neuronal "supernetworks" may cooperatively entrain large populations of pyramidal cells throughout the forebrain. Experiments on hippocampal interneurons are reviewed and possible solutions for some of these complex functions are illustrated.