Integrating information from the auditory and visual modalities is vital for speech perception. In this thesis, I describe two studies of audiovisual speech perception that make use of an audiovisual illusion known as the McGurk effect. In the McGurk effect, two different syllables presented simultaneously in auditory and visual modalities are fused and perceived as a novel syllable (McGurk & MacDonald, 1976). In the first study, we conducted a large-scale assessment of the McGurk effect across fourteen McGurk stimuli tested in up to 165 participants. This study revealed that McGurk perception is characterized by wide variability across stimuli. The second study investigated whether phonetic identification training could increase McGurk perception. This study showed that participants improved on the training task, but there was no increase in McGurk perception.