The Nikon D3S is a 12.1 megapixel professional-grade full frame (35mm) digital single-lens reflex camera (DSLR) announced by Nikon Corporation on 14 October 2009. The D3S is the fourth camera in Nikon's line to feature a full frame sensor, following the D3, D700 and D3X. It is also Nikon's first full frame camera to feature HD video recording. While it retains the same number of pixels as its predecessor, the imaging sensor has been completely redesigned. Nikon claims improved ultra-high image sensor sensitivity with up to ISO 102400, HD movie capability for extremely low-lit situations, image sensor cleaning, optimized workflow speed, improved autofocus and metering, enhanced built-in RAW processor, quiet shutter-release mode, up to 4,200 frames per battery charge and other changes compared with the D3. It was replaced by the D4 as Nikon's high speed flagship DSLR.

Many independent reviews and comparisons show that image noise was improved up to 2 stops compared to the Nikon D3 or D700. Other functions, especially autofocus and speed, support this, causing PhotographyBlog to conclude: “hand-held photography anytime, anywhere, without flash”. There are comparisons with the Canon EOS-1D Mark IV, which is rated 1.3 stops lower by DxOMark on their low-light ISO score (1320 ISO vs. 3253 ISO for the D3s).