Background: Teacher self-efficacy has received attention because of its direct relationship with teachers' classroom behaviors. Since engineering has been increasingly introduced in K-12 (precollege) education, development of an instrument to measure teachers' self-efficacy in the context of teaching engineering has been needed. Purpose (Hypothesis): This study reports the development and validation of the Teaching Engineering Self-Efficacy Scale (TESS) for K-12 teachers. Design/Method: The items for the TESS were constructed through a comprehensive review of the literature regarding K-12 engineering education, the development of teachers' self-efficacy instruments in STEM areas, and K-12 teachers' reflections on integrating engineering into their classrooms. During the content and face validity process, we used structural equation modeling to identify and confirm the factor structure of the TESS, and used item-analyses for reliability evidence. Results: With data from 434 teachers in 19 states, exploratory and confirmatory factor analyses using structural equation modeling resulted in the TESS consisting of 23 items loading across four factors: engineering pedagogical content knowledge, engineering engagement, engineering disciplinary self-efficacy, and outcome expectancy. Cronbach's [alpha] ranged from 0.89 to 0.96 and exhibited high internal consistency reliability coefficients for the TESS. Conclusions: Teacher self-efficacy is a situation-specific construct because teachers' efficacy beliefs depend on the content area and teaching environment. Use of the TESS, as an instrument tailored for the engineering teaching context, can contribute to the literature on K-12 engineering education and improve the teaching of precollege engineering.