In the first part of the Dissertation, we focus on analyzing whether a incumbent can use quantity discounts to deter a more efficient but capacity constrained rival from entering the market. Although entry can profitably be deterred, the incumbent's optimal strategy is to accommodate entry. In a dynamic framework, when the incumbent faces sequential entry by short-lived entrants, we find that entry deterrence is an equilibrium of the infinitely repeated game if the discount factor is large enough. In the second part of the Dissertation, we have analyzed price competition in duopolistic segmented markets when each firm has a loyal customer base. Loyal customers buy only from the firm to which they are loyal. The unique equilibrium of the ...