Oscillations in the brain are now being studied by a large variety of methods, have been observed in most brain regions and have been implicated in a variety of processes. Yet, a substantial fraction of the neuroscience community does not think oscillations are fundamental to brain function. I will argue that oscillations are fundamental to the operation of sensory, memory and motor systems. This argument is based on the following: 1) That the question of which cells in a network fire can only be understood once one takes into consideration the fact that inhibition is oscillatory (at gamma frequency). Importantly, the rule that determines which cells fire is not cell autonomous (cannot be determined by the inhibitory and excitatory input to that cell), but depends on the entire network, which produces a type of winner-take-all computation. 2) Oscillations at different frequencies interact, the best example being theta and gamma frequency oscillations. The resulting theta-gamma code organizes multi-item messages. Each item is represented by an ensemble of cells that show synchronized firing during a gamma cycle. This code is now clearly demonstrated in the hippocampal region and its target structures (PFC and striatum). However, I will present evidence that it is also relevant to sensory processes.