In the development of the Next Generation Science Standards (NGSS) there was a purposeful effort to not only include but prioritize science and engineering practices as part of the standards. Including the science and engineering practices in science curriculum and instruction is thought to help students understand how scientific knowledge develops and embed this knowledge in their worldview (3 Dimension 1: Scientific and Engineering Practices, 2012). Epistemic cognition, the concept of how one views knowledge and what beliefs they hold about knowledge, has been found to have significant influences on learning and academic success (Cano, 2005; Greene et al., 2018; Schommer, 1990). This study utilized a self-report survey and presents the results of mixed-methods both quantitative and qualitative analysis to identify and bring saliency to correlational relationships between recent U.S. high school graduates' self-perceptions in their ability to perform the eight NGSS science practices and two dimensions of epistemic cognition (source and structure of knowledge) and between the dimensions across domain specificity. Undergraduate college students were recruited to complete a scenario-based survey intended to elicit both general and science-specific domain epistemic beliefs as well as rank their self-perception in their ability to perform the eight NGSS science and engineering practices (SEP). Findings from this study indicate that these students' self-perceptions in performing the SEP were correlated to a number of source and structure beliefs both in science-specific knowledge and knowledge generally or as an unspecified concept. Participants use multiple sources and justificatory standards when encountering science knowledge contexts. Engaging in the SEP may help students to develop sophisticated conceptualizations of science knowledge and components of both science-specific and general epistemic cognition. [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.]