Conservation laws are very important in quantum physics. Two examples of applications will be given. First, optical pumping which uses transfer of angular momentum from polarized photons to atoms to produce highly polarized atomic gases. Then, laser cooling which uses transfer of linear momentum from photons to atoms to produce large forces, allowing one to cool these atoms at extremely low temperatures and to get atomic gases with quantum properties. Various applications of optical pumping and laser cooling will be briefly reviewed showing how long term basic research is essential for improving our understanding of the world and for giving rise to a wealth of important applications.