Depending on experimental conditions, adsorbed polymer layers on particles can either increase or decrease the stability of a collidal dispersion. The aggregated formed in the latter case are called flocs. Numerous macroscopic techniques are used to clear up the factors that control their formation and it appears that flocculation of suspensions by addition of macromolecules proceeds via various mechanisms form bridging to charge neutralization according to the kind of the polymer‐particle interaction. The organization of the particles inside the aggregates is examined by small angle neutron scattering (SANS). It is mainly governed by the remaining interparticle repulsions. Different structures can be observed when these repulsions decrease: linear necklaces branched clusters, tridimensional aggregates with short range liquid like order and finally fractal objects when the surfaces can be brought to contact.