Cognitive control requires binding packages of information (e.g., stimulus-response bindings) together on the fly, often for just a brief period. However, it remains unclear how humans can do this. We propose that neural oscillations at theta frequency (4-8 Hz) are key in this respect. We present a computational model of how theta can synchronize specific neural modules. Thus, the model can functionally construct the required packages of information depending on the task at hand; and quickly dismantle them when no longer needed (e.g., in the next trial). In this model, theta amplitude and theta frequency are two dimensions that can be controlled for optimal cognitive control. Empirically, we demonstrate that theta amplitude correlates with model predictions; and that increased amplitude relates to increased neural synchronisation (as measured with EEG), presumably to create the required packages of information. The model predicts that theta frequency decreases when a more difficult task is upcoming, because slower theta waves allow more time for competing representations to settle. This decreased frequency should be visible in both neurophysiology (measured via EEG) and in behavior (measured via accuracy). In line with model simulations, we find empirically in the EEG spectrum that a cue predicting an upcoming difficult (relative to easy) stimulus, decreases theta frequency. Similarly, theta frequency measured at the behavioral level is slowed down on such difficult stimuli. This result demonstrates how different aspects of theta oscillations (amplitude and frequency) can be recruited for cognitive control, and how they can be manifested in EEG and behavior.