Disclosed are a quantum dot and a quantum dot-polymer composite and a device including the same, wherein the quantum dot includes a semiconductor nanocrystal core including indium (In) and phosphorous (P), a first semiconductor nanocrystal shell disposed on the semiconductor nanocrystal core, the first semiconductor nanocrystal shell including zinc and selenium, and a second semiconductor nanocrystal shell disposed on the first semiconductor nanocrystal shell, the second semiconductor nanocrystal shell including zinc and sulfur, wherein the quantum dot does not include cadmium, wherein in the quantum dot, a mole ratio of sulfur with respect to selenium is less than or equal to about 2.5:1.