In order for the U.S. to continue its superiority and competitiveness in science and technology worldwide, it will need to produce one million more graduates in science, technology, engineering, and mathematics (STEM) subjects than it is currently expected over the next decade. One of the national priorities of the U.S. education system, therefore, has been to supply a sufficient number of graduates in the STEM fields. Of the main obstacles that prevent college students from majoring in the STEM fields are the students' mindset and lack of motivation. The purpose of this mixed-methods study was to examine the influence of motivation and mindset interventions on students majoring in STEM fields in order to enhance and improve the students' success in their pre-calculus course. The study included both quantitative and qualitative research questions. To answer the quantitative research questions, three instruments (i.e., PCA, SMQ-II, and the Mindset Survey) were used. The analysis of the PCA and SMQ-II scores, using ANCOVA for controlling the pre-existing differences in pre-test scores, indicated no statistically significant difference between the two groups in terms of pre-calculus achievement and motivation toward learning mathematics. When comparing the two groups at post-test with regard to mindset, there was a difference in the proportion of participants with a growth mindset toward intelligence (3%) and mathematical ability (10%), where the experimental group had the higher proportions. In addition, there was an increase in the proportion of participants in the experimental group with a growth mindset toward intelligence (27%) and mathematical ability (4%) from pre- to post-interventions. Qualitative data such as interviews, written reflections, and classroom observations were used to answer the qualitative research question. Although all case study participants perceived benefits from the motivation interventions, they did not report a change in their motivation toward learning mathematics. All case study participants, whether they started out with a growth or a fixed mindset, perceived themselves to have a growth mindset toward intelligence and mathematical ability after the interventions However, it was not clear whether the interventions were effective enough for the students to maintain the growth mindset beyond the semester of study. [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.]