The complexation of polyelectrolytes is very attractive to process polysaccharides into biomaterials, because it is energy efficient, requires no toxic chemical, has a low environmental impact and can be applied to biocompatible polymers such as polysaccharides. We used chitosan, a copolymer of Nacetyl glucosamine and glucosamine obtained from the partial deacetylation of chitin as polycation and a variety of polyanions such as dextran sulphate, hyaluronan, heparin, chondroitin sulphate. These polysaccharides are generally regarded as safe and some of them can be found in the extracellular matrix of In this contribution we will present our latest achievement in the control of the elaboration, structure and performances of polyelectrolyte nanocomplexes as drug and vaccine carriers of high potential. In particular, we will address the issues of colloidal stability in physiological media, a major limiting factor in the development of this technology; the nanocomplex loading with drugs or vaccine; the targeting of these nanodelivery systems. The formation of polyelectrolyte complexes is spontaneous at room temperature, i.e. under kineticds control. We will present an alternative approach close to the trmodynamic equilibrium and discuss the potentiality of this particularly innovative synthesis route. Finally, we will present our latest results on the delivery of anti-retroviral drug and the inhibition of the infection by the HIV-1 virus of hPBMCs in vitro. The delivery of vaccine will also be shown.