This descriptive case study aimed to understand the perception and needs of Michigan public high school science teachers during the implementation of the Next Generation Science Standards (NGSS) and subsequent preparedness to teach the content found in the new curriculum. A questionnaire was distributed to science teachers state-wide, with twenty teacher respondents from across the state-wide population of certified public school science teachers. Sixteen individual interviews and one focus group comprised of four teachers were used to collect additional data. The data were coded then analyzed using a thematic analysis process. There was a gap in the literature regarding the experiences and needs of Michigan high school science teachers implementing the NGSS, which this study addressed. Bandura's self-efficacy theory and Fiedler's contingency theory framed this study. This study investigated the perceptions Michigan high school science teachers have regarding the implementation of the NGSS, their description of preparedness to teach the NGSS, and the processes and strategies used during the implementation of the NGSS. Five themes emerged from the thematic analysis: teacher customization of the curriculum to fit their individual needs, differences in implementation between "NGSS Natives" and "HSCE Converts," the need for professional learning about the NGSS, the need for additional resources, and the implications due to the lack of leadership throughout implementation. Areas of recommended further study include the differences between NGSS Natives and HSCE Converts, the fidelity of implementation of the engineering and Earth science standards, and 3D Assessment in the classroom. [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.]