For over 60 years, speech perception researchers have investigated listeners' ability to resolve the linguistic information encoded in input acoustic signals. More recent investigations have also explored listeners' resolution of the indexical information that is carried in the same signal. Both lines of study (and their important intersection) point toward the remarkable adaptability of perception. Listeners not only achieve perceptual stability across many types of variation, they also use that variation as important information about what a speaker is saying and about who said it. This course focuses on the malleable, dynamic nature of speech perception. We will consider contemporary theoretical approaches to the dynamics of speech perception as it unfolds in real time and as it evolves with experience and learning, and will assess these approaches in relation to both classic and recent experimental findings. We will consider as well how the dynamics of speech perception might serve as a phonetic impetus for sound change.