Several of current models of speech perception assume an important role of endogenously rhythmic brain activity for the processing of speech. However, demonstrating a causal role of brain rhythms for such functions can be challenging, due to alternative processes that can produce similarly rhythmic patterns in perceptual or neural data. In this talk, I will summarise results from experiments using acoustic and electric entrainment to reveal endogenous brain rhythms causally modulating speech perception. Most of these are based on the notion that rhythmic brain responses are more likely to involve endogenous rhythms if they persist after the offset of a rhythmic stimulus. I will further show that most of the findings seem specific to intelligible speech, corroborating the important role brain rhythms and their entrainment play for speech processing.