In an effort to improve an understanding of content area vocabulary instruction and how to support teacher-educators, in this study I sought to determine which vocabulary instructional practices were selected from the corpus and applied in instruction. I examined the knowledge and beliefs held by the participants about vocabulary instruction in their respective disciplines. In addition, I worked to determine the sources from which teachers acquire information to professionally proceed with the vocabulary instruction that does occur. Using a mixed methods design, I studied grades 6-12 science, social studies, and technical studies teachers' beliefs about, and conceptions of, vocabulary instruction. While there has been increased attention to teaching vocabulary (Baumann, 2009; Blachowicz & Fisher, 2010; Fisher & Frey, 2014; Graves, 2006; Manyak et al., 2014; McKeown et al., 2018; Nagy & Townsend, 2012), little is known about how content area teachers conceptualize teaching their respective discipline-specific terminology. Therefore, the goal is to add to the existing knowledge base in academic disciplines via an examination of how teachers' beliefs and conceptualization and enactment of the specific instructional practices in vocabulary. [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.]