Polyolefin surfaces are characterized by their chemical inertness. To improve the adhesion property of polyolefins using flexible spacer molecules on their surface or to produce biosensitive surfaces by grafting brushes, combs, dendrimers, proteins, and other biomolecules with bioactivity, biosensor, or antifouling properties, the presence of anchoring points at the polyolefin surface for grafting these molecules is necessary. More precisely, the existence of only one sort of functional groups in sufficient concentration at polyolefin surfaces is a precondition for chemical grafting of such biomolecules or polymer molecules onto these monosort groups. Several routes for the introduction of monotype functional groups are based on plasma treatment. However, it is well known that plasma treatment is a priori not selective. Therefore, new plasma processes with high selectivity in producing monotype functional groups were developed, alternatively combinations of plasma and chemical treatment were used, or the polyolefin substrates were coated with thin layers of functional groups bearing polymer layers produced by plasma polymerization or electrospray ionization (ESI). Grafting was preferentially performed in a way by nucleophilic substitution of the graft molecule onto the monotype functional groups at polyolefin surfaces. This entry covers the energetic situation in plasmas, the dissociation energies in polyolefins, the oxidation of polyolefin surfaces, the broad variety of produced oxygen-containing groups, and side- and post-plasma reactions. A few ways to introduce such monotype functional groups are explained in more detail as well as proven and tested graft reactions. Alternative plasma and film deposition processes are introduced.