Duncan's interests span most of extragalactic astronomy and cosmology, however his focus is on observational aspects of galaxy formation and evolution. He is taking a leading role in the international SAGES project (Study the Astrophysics of Globular clusters in Extragalactic Systems) which combines HST and Subaru imaging with Keck spectra to better understand globular cluster systems. Duncan regularly observes on the Keck and AAT telescopes and he has previously worked at the Hubble Space Telescope Science Institute.