The modification of a polypropylene surface in a nitrogen plasma is studied in terms of degradation, crosslinking, functionalization, and activation (radical site creation.) The most important reactions are functionalization through primary amine formation and radical creation through methyl-group elimination. Degradation and crosslinking are competitive and the latter is more important when the plasma conditions (exposure time, discharge power) are severe. Exomethylenic bonds (CH2=C) are formed preferentially over crosslinking reactions. Chemical titrations are described for radical and amine concentrations on the polypropylene surface.