Light Scattering Let us consider a suspension of objects in a solvent such that the dielectric constant of the objects is different from that of the solvent. Then, when the suspension is illuminated with an electromagnetic wave, the objects in suspension diffuse light. If their concentration is low enough, the diffused intensity in any direction will be due to a single object. This is the quasi-elastic light scattering limit. It is possible to detect: (i) the variation of the diffused intensity as a function of the direction (static diffusion), (ii) the intensity fluctuations as a function of time, in a given observation direction (dynamic light scattering). These measurements allow to determine the size of the objects in solution. Reciprocally, if their size is known, one deduces from such measurements the viscoelastic properties of the suspending medium (micro-rheology measurements).