Since 1980, the number of people in the United States who speak a language other than English at home has increased by 140% (United States Census Bureau, 2010).Therefore a greater percentage of students now are multilingual. Throughout the world, multilingualism is considered the norm and monolingualism is the exception (Auer & Wei, 2008). In the United States, however, policies regarding instruction in schools are still influenced by monolingual ideology that carries expectations and assumptions of assimilation, loss of mother tongues, and defined hierarchical structures. As classroom populations become socially, ethnically, racially, and linguistically more diverse, it is increasingly important for teachers to have an understanding of how to address diversity in schools and for educators to understand how language use and the teachers' role in the classroom impacts learning. This paper explored the existing language beliefs and linguistic knowledge of preservice teachers as they prepare to enter linguistically and culturally diverse classrooms. The increasing prominence of cross-cultural interactions creates a necessity for teachers to develop intercultural competence. Employing a conceptual framework of intercultural communicative competence theory, this qualitative study investigated experiences and knowledge in linguistics that influence teacher speech acts.Research in fields of applied linguistics such as psycholinguistics, neurolinguistics, sociolinguistics, and educational linguistics revealed basic language knowledge that teachers need before they enter diverse classrooms including knowledge Linguistic Diversity ii of language acquisition, phonology, syntax, semantics, pragmatics, culture, instruction language, and how the brain processes language. The literature from these fields was used to create an instrument that included a demographics questionnaire, beliefs survey, linguistic knowledge assessment, and interview questions. Twenty-three preservice teachers participated in the study to describe their language beliefs and knowledge.Many of the findings in this study reflected key-findings in the literature; however, this study also found several significant findings that extend existing research.The results revealed significant impacts of 1) individual experiences with culture and linguistic contact, 2) the language used in classrooms, specifically languages other than Standard English and the deep and surface structure of language, 3) linguistic knowledge, specifically phonology, 4) meta-cognitive behavior and reflection, and 5) differences between monolingual and multilingual preservice teachers. The data also indicated that the majority of preservice teachers were concerned about preparedness in teaching in diverse classrooms. Implications for teachers working in culturally and linguistically diverse classrooms and for teacher preparation programs are discussed.Linguistic Diversity iii Dedication