F0 contours convey multiple types of information, including lexical and post-lexical meanings, as well as affective and socio-indexical indicators. This dissertation investigates the interaction between lexical tone and sentence-level intonation in Thai, focusing on how sentence position influences the acoustic realization and perceptual categorization of tone and what this reveals about the underlying phonological representation of tone. To explore these questions, three experiments were conducted to examine the perception and production of High and Falling tones in sentence-medial and sentence-final contexts. Chapter I provides a general introduction, framing the research questions and dissertation goals. It includes a brief overview of existing research on Thai tone and intonation, as well as the interaction between the two. In Chapter II, the categorical perception of High and Falling tone in sentence-medial versus sentence-final positions is tested using classic identification and discrimination tasks (Experiment 1). An original contribution of this study is the use of whole-sentence stimuli containing target words synthesized along tone continua to simulate ecological validity and provide acoustic context. The results from these tasks demonstrate clear categorical perception of the target tone words and reveal an effect of intonational context, in which the categorical tone boundary shifts depending on context. Chapter III details a production study (Experiment 2), where multiple participants read aloud sentences placing target tone words in either medial or final context. Analysis of these productions shows minimal variation between participants. It also confirms an effect of intonational context, with words in the sentence-final position exhibiting a global lowering effect due to the associated low boundary tone (L%). Chapter IV describes a word recognition task using eyetracking in the Visual World Paradigm (Experiment 3) to test the online perception of tone words in different sentence contexts. Results from Experiments 1 and 2 suggested that there are specific acoustic landmarks that lead to tonal recognition, and so it was hypothesized that cues such as F0 peak alignment would trigger eye fixations toward a target word. Results from this experiment showed very early and rapid fixations to a target word, as the High and Falling tone words used in the experiment were immediately distinguishable at the onset of the audio stimulus. Chapter V presents a general discussion. The overall combined findings of the three experiments align with predictions that tone and intonation interact in a way that affects not just acoustic realizations but also perception. Implications for underlying phonological representations and processing of suprasegmentals are also discussed, as are potential future directions for future research. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]