This feature article deals with the self assembly and physical chemistry of polyelectrolytes: multilayers and brushes. The article highlights the interesting behavior of polyelectrolytes in nanoscale assemblies, giving more insight into the complexity of the formation of the assemblies. The water content of multilayers and brushes is studied during the assembly and in different ionic strengths. Similarities are found in the behavior of the brushes and multilayers with ionic strength, with regard to changes in the thickness and the water content. An invariance of the zeta potential with ionic strength is also observed for both systems, which can be explained as a result of conformational changes of the polymer chains. Finally, the combination of brushes and multilayers for surface modification is presented.