Average faculty salaries differ widely across fields at American colleges and universities and the magnitudes of these field differences in salaries have been growing over time. What is less well known, however, is that at any point in time there are wide differences in the magnitudes of field differences in faculty salaries across academic institutions. Our paper uses institutional level data by field on average faculty salaries, which we were granted access to by the universities that participate in a national data exchange, to analyze why these differences across institutions exist. Our main finding is that differences in the quality of faculty present in different fields at a university, as measured by differences in the national research council ratings of graduate programs at the university, are important predictors of the field differences in average faculty salaries that exist at the full professor level at the university.