Noise in biological systems is inevitable. Already more than 60 years ago, it was realized by E. Schrödinger that "incredibly small groups of atoms, much too small to display exact statistical laws, do play a dominating role in the very orderly and lawful events within a living organism" (What is life?, 1944). Clearly, in processes such as the segregation of chromosomes during cell division, cells have evolved specific mechanisms to reduce the noise that would perturb cellular processes.

The analysis of the way cells either fight against or amplify noise has led to new insights into the design and evolution of genetic networks. Recently, the tremendous advances in experimental methods taken from various fields have enabled the direct evaluation of the noise level and its effect on biological systems. We will review experimental approaches to the study of the causes and consequences of noise in biological systems.