A thermal imager (also called an infrared camera or thermographic camera) is a device that forms an image using infrared radiation, similar to a common camera that forms an image using visible light.

Instead of the 400-700 nanometre range of the visible light camera, infrared cameras operate in wavelengths as long as 14,000 nm (14 µm). Their use is called thermography. 

Images from infrared cameras tend to be monochrome because the cameras generally use an image sensor that does not distinguish different wavelengths of infrared radiation.