Background: Students are more likely to persist when they both perceive themselves as capable of success (expectancy) and perceive tasks to be interesting, important, and useful (values) or less costly in terms of effort, lost opportunities, and psychological stress (perceived costs). Prior research has not examined whether these motivational beliefs synergistically predict engineering-related outcomes; studying such synergy is critical for understanding how multiple forms of motivation combine to support engineering persistence. Purpose/Hypothesis: We tested how engineering academic self-efficacy (expectancy), values/costs, and their interaction predicted engineering-related outcomes. We hypothesized that there would be significant interactions between self-efficacy and values/costs in predicting engineering persistence and academic success. Design/Method: Structural equation modeling was used to investigate latent interactions between self-efficacy and values/costs (interest, attainment, and utility values; opportunity, effort, and psychological costs) in predicting career intentions, aspirations for engineering graduate school, and engineering retention, and grades in foundational courses for engineering among first-year engineering undergraduates (n = 2420). Results: Significant interactions between self-efficacy and values (interest and utility only) were identified, but not for self-efficacy and attainment value or costs. Feeling both competent in engineering and highly valuing engineering were simultaneously related to higher engineering persistence, as compared to either feeling competent or valuing engineering alone. Conclusions: The findings contribute to expectancy--value theory by providing a more precise understanding of the role of each type of value and cost in predicting distal outcomes, and practicing by highlighting the importance of supporting both expectancy and values when intervening to support engineering persistence.