Ambiguity is a natural part of language and in studying the comprehension and resolution of ambiguity in a second language (L2), we must consider the influence of the native language. This dissertation examines L2 processing of the lexical semantic ambiguities, homonyms and polysemes. These are words that share the same form but have different meanings (homonyms) or senses (polysemes). In the literature, there is a documented "ambiguity advantage" where ambiguous words have been observed to be processed faster than unambiguous words. In particular, this effect has been attributed to the difference between polysemes and homonyms. Work on these ambiguities is largely done for first language (L1) processing, but currently there is little work on this with L2 speakers in the processing literature. The dissertation considers various aspects of the L2 experience which include changes to the lexicon based on proficiency and issues of language selectivity, that is, activation, and how they contribute to the processing of homonyms and polysemes in a non-native language. Experiments conducted also test what occurs when ambiguities are and are not shared across the native and non-native languages. The dissertation presents a series of experiments where homonyms and polysemes are placed without context in a lexical decision task, as well as in a sentence context in a self-paced reading task. In a lexical decision task performed in the L2, higher proficiency L2 speakers produced a polysemy advantage for both their second language as well as for polysemes exclusive to their native language. Yet, in the self-paced reading task, the effect instead becomes a polysemy disadvantage, unlike for native speakers. While there are similarities between L2 and native speaker processing, the differences found across all experiments reflect the unique contribution of the native language. It is clear that the L1 plays a prominent role in L2 processing, though processing can become more "native-like" in the L2 with increasing proficiency. The results found here highlight aspects of L2 lexical learning and access as well as a need for continued research of L2 ambiguity processing under varied experimental conditions. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]