Understanding the nature of light and its interactions with matter has always been a challenge for Physics. New concepts have emerged from these investigations, such as the quantum nature of the microscopic world and the wave particle duality. Light is an essential source of information on the world around us, not only at the microscopic scale of atoms and molecules, but also at the very large scale of the universe. It appears now that light is also a powerful tool for acting on atoms, for manipulating them, for polarizing them, for cooling them at very low temperatures. A brief review will be given of recent developments in this field, including very precise atomic clocks, the realization of new states of matter such as Bose-Einstein condensates, matter waves and atom lasers.