Résumé : Irreversibly adsorbed polymer layers represent an intriguing new class of materials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. These extremely thin layers (thickness < few tens of nanometers) are obtained via a short list of successive steps, easily reproducible in a laboratory environment: a polymer melt is placed in contact with an adsorbing substrate and non-adsorbed chains are washed away by soaking the sample in a good solvent. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying the performance of polymer coatings without affecting the interfacial chemistry. Here, after providing an introduction to the kinetics of irreversible adsorption, we discuss on the most commonly used methods to determine the thickness of adsorbed layers. We conclude with a brief perspective on future possible applications of adsorbed layers.