Building on previous studies of multiple text reading in history, this study aimed to contribute to that body of work by focusing on non-traditional multimodal sources. In an age of rapidly increasing access to and use of multimodal sources and a demand for reading and comprehending increasingly complex and specialized texts, it appeared there was a gap in the research that this study could help to address. This study used mixed methods to investigate 1) how students read multiple multimodal sources, 2) how those multimodal sources influenced students' historical reasoning, 3) how students used multimodal sources to respond to a historical inquiry question through an argumentative essay, and 4) how individual learner characteristics like prior knowledge, interest, and reading ability contributed to students' ability to construct an argument after reading multiple multimodal sources. Fifty-one students in two high school history classes participated in the study. Forty-three students completed a three day inquiry task, using a single website to read eight multimodal sources about the Gulf of Tonkin Incident and wrote an essay. Eight students completed think-aloud protocols while reading the same eight multimodal sources and participated in a semi-structured interview immediately following the think-aloud protocol. Data was analyzed for historical thinking processes, the ways multiple sources influenced student thinking, the ways students used multiple sources in their essays, and how prior knowledge, interest, and reading ability contributed to their ability to create a historical argument using multiple multimodal sources. The results of this study suggest that the use of multimodal sources in historical inquiry may benefit less proficient readers. The study also demonstrated that students could reason with complex historical sources. Despite the complexity of thinking revealed by students, it is also evident that multimodal sources cannot just be added to the curriculum. Disciplinary literacy strategies are necessary to help foster critical and integrated reading of complex historical sources. Multimodal sources did not help students to write high quality arguments either. Teacher scaffolding of writing for argument is critical regardless of the text types used for inquiry. [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.]