In conversation, speakers produce some words with greater intensity, longer duration, and higher fundamental frequency (F0) than other words. By making different words in a sentence more prominent than other words, a speaker can change the meaning implied by a sentence. This thesis explores the relationship between processing in the language production system and the prominence of referring expressions. In particular, this thesis focuses on the effect of processing at the message and lexical levels of language production. Across seven experiments, I examine three factors that affect prominence: predictability, repetition, and partner identity. Based upon these the results, I argue that these factors can be separated into factors that operate at the level of the message and factors that operate at the level of lexical access. Furthermore, the results suggest that message level factors and lexical level factors affect prominence in different ways: lexical level factors lead to differences in spoken duration cross-linguistically whereas message level factors manifest differently across different languages. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]