In this paper we analyze firms' ability to tacitly collude on pricesin an infinitely repeated duopoly game of vertical productdifferentiation. We show that firms collude if and only if their discountfactor is high enough, i.e. if they value future profits sufficiently. We alsoshow that a lower cost of copying facilitates collusion but that a higherquality of the copy hinders collusion. Thus, the overall effect of thesenew characteristics of copies made by consumers is ambiguous.