All students must graduate high school with the knowledge, skills, and competencies needed to succeed in today's world. One of the most current educational reform efforts to meet this goal is the development and implementation of the Next Generation Science Standards (NGSS), which guides learners to achieve success in solving real-world problems while incorporating science content, engineering practices, and 21st-century skills. The NGSS is the expectation that all students should aim to make intelligent decisions about how science impacts the population and Earth. This mixed methods study uses the theoretical framework of self-efficacy to answer the research question: How do self-efficacy and science beliefs contribute to implementing the NGSS in high school science classes? Although many states, including Maryland, have moved towards adopting the NGSS, many teachers, administrators, and district officials are looking for assistance with integrating and implementing the new three-dimensional learning design. Through an electronic survey and personal interviews, the study reveals that self-efficacy does not have as significant a role in implementation as the teachers' science beliefs. Teachers' self-efficacy in the content they teach is higher than when they are not comfortable with other science disciplines. The correlation between the two aspects overall slowed the NGSS integration. To overcome the obstacle of science beliefs, teachers shared that professional development, professional learning communities, and district initiatives assisted in implementing the NGSS framework. From the responses collected, the lived experiences of the science educators show the need for administration and district officials to amend the current practices allowing for more accountability, modeling of the district NGSS curriculum, and time for a change. Successful NGSS implementation is possible with the support the teachers ask for and if they are willing to revise their science beliefs. Improving science educators' self-efficacy and science beliefs will improve science for all students. Keywords: science self-efficacy, teacher efficacy, science beliefs, science education, science curriculum, science standards, NGSS, transformational teaching. [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.]