In this thesis the model of a payment card network is constructed to explore the impact of downstream market characteristics (i.e., the market where merchants and consumers interact) on the merchant and the interchange fee, thereby extending the literature’s observations of payment systems. To accomplish this, three scenarios are analyzed: firstly, a unitary payment card network with merchants under Cournot quantity competition and, secondly, under Bertrand price competition respectively, as well as, thirdly, a multi-party payment card network with merchants under Cournot quantity competition. This study yields two significant results. Firstly, the merchant and the interchange fee are found decreasing in the consumer price elasticity, the l...