Psychological theories of motivation and performance are relevant to teaching and learning in the science, technology, engineering, and mathematics (STEM) disciplines. The present study applies Dweck's mindset theory of motivation to an examination of the relationship among instructor mindset, instructor motivational attitudes, and the use of effective teaching practices. Faculty members who teach undergraduate courses in STEM disciplines completed a survey designed to assess fixed versus growth mindset, mastery orientation (measures of motivation and efficacy), and teaching practices. Results supported a model consistent with Dweck's theory of motivation, whereby mastery orientation mediates the relationship between instructor mindset and teaching behaviors. It appears that this psychological theory of motivation may be helpful in understanding teaching and learning in STEM disciplines. More research using a variety of measures and teaching contexts is necessary before full applicability can be realized.