Educators in the social studies content area have struggled for over a century with how to best instruct their students in critical thinking. A growing group of researchers in the discipline of history, one of the major components of social studies education, support teaching the domain-specific skills of historical thinking through the process of historical inquiry. Nevertheless, many social studies teachers lack the pedagogical content knowledge to instruct their students in historical thinking skills through historical inquiry. This multiple case study sought to examine how two social studies teachers might change their knowledge, beliefs and practices after engaging in a historical inquiry professional development. The professional development incorporated many of the characteristics of effective teacher learning opportunities. The theoretical frameworks for the study included social constructivist learning theory, expert/novice learning theory, and teacher change theory. Analysis of data from teacher and student interviews, teacher surveys, classroom observations, teacher reflective journals, artifact review, and audio recordings of the professional development sessions revealed significant patterns within and across the two case study participants. Changes observed in the teachers' knowledge, beliefs and practices indicated they were able to instruct their students in historical thinking skills through historical inquiry within their respective curriculums. However, both teachers faced the challenges of curriculum design, time constraints, as well as students' varied development and motivation levels. Findings from this study have implications for how to support social studies teachers as they develop pedagogical content knowledge in historical inquiry in order to teach their students historical thinking skills. [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.]