The present technology relates to an image sensor, an imaging device, and a ranging device capable of performing imaging so that noise is reduced. A photoelectric conversion unit configured to perform photoelectric conversion; a charge accumulation unit configured to accumulate charges obtained by the photoelectric conversion unit; a transfer unit configured to transfer the charges from the photoelectric conversion unit to the charge accumulation unit; a reset unit configured to reset the charge accumulation unit; a reset voltage control unit configured to control a voltage to be applied to the reset unit; and an additional control unit configured to control addition of capacitance to the charge accumulation unit are included. The charge accumulation unit includes a plurality of regions. The present technology can be applied to, for example, an imaging device that captures an image and a ranging device that performs ranging.