Quantum coherence is important for nonlinear optical properties of atomic and molecular media, as well as semiconductor nanostructures. The coherent effects lead to transparency of opaque media and allow one to enhance nonlinear optical effects. In my presentation we are going to discuss the temporal and spatial properties of atomic coherence, its role and fundamental limits, as well as possible applications. The spatial coherence will be discussed in relation to the developing of new coherent sources of radiation. We show the cooperative resonance that allows us to generate the coherent radiation together with simultaneous excitation of the atomic media.