Oscillations of the electric field generated by neuronal populations are often observed in intracranial EEG recordings from human cortical and subcortical brain regions. The functional relevance of these oscillations for neural processing and cognitive functions remains a debated issue in modern neuroscience. In this chapter, we review evidence that iEEG oscillations constitute a key mechanism in the functional integration of neuronal activity across temporal and spatial scales. We focus on the potential role of cortical oscillations in cognitive processes, and particularly speech perception and production, which involve diverse brain regions and temporal scales in a structured hierarchy, as an ideal testbed for outlining the possible insights that iEEG oscillations offer on cognitive functions.