The adhesion between plasma-modified polyethylene (PE) and different polar polymers, as well as aluminium and steel, has been studied. The PE was modified by either oxygen plasma treatment or plasma polymerization of acrylic acid. The results show the importance of introducing polar groups on the surface of the non-polar PE in order to improve the adhesion to polar polymers as well as metals. Laminates made of plasma-modified PE and polyamide 6 (PA-6) or poly(ethylene vinyl alcohol) (EVAL-G) showed failure in PA-6 or EVAL-G when delaminated. Poly(ethylene terephthalate) (PET), which is not as polar as PA-6 or EVAL-G, showed an adhesive failure when the PE was treated with either of the plasma methods. However, when both the PET and the PE were modified, the failure occurred in the PET upon delamination. Oxygen plasma treatment of PE resulted in an increased adhesion when laminated with cellophane, with no observed material failure. The laminates composed of plasma-modified PE and aluminium or steel showed cohesive failure in the PE.