The present technology relates to an image sensor and an electronic apparatus which can make the image sensor a smaller without degrading performance of the image sensor. The image sensor includes a pixel array unit in which pixels including photoelectric conversion elements are arranged in a two dimensional manner, a row circuit configured to control row scanning of the pixel array unit, and a column processing unit configured to convert an analog signal read out from the pixel array unit into a digital signal. The pixel array unit is disposed on a first-layer substrate, and the row circuit and the column processing unit are disposed on different substrates which are underlying layers of the first-layer substrate and which are laminated on the first-layer substrate. The present technology is applicable to the image sensor.