Means of exchange holding legal tender are not the unique means of payment that materialize currency. Any device accepted by the creditor enables exchanges, even when different instruments have different scope of liquidity and diverse broadness of acceptance. Therefore, admission by economic actors appears to be the ultimate criteria to embody monetary attributes into a material instrument, conferring its function as means of payment. In this sense, the agency of involved actors is critical to understand the emergence of new financial devices derived from institutional changes. This chapter aims to examine the appearance and diffusion of a new means of payment, the bank check, in the early nineteenth-century economy of South America, specifically Buenos Aires. As the main issuers of checks gained leverage in using this means of payment, they contributed to enhancing its acceptance in the local economy. To demonstrate this hypothesis, this chapter employs Social Network Analysis tools to understand the relational structure of the check’s flows and elucidate the position of the actors within that web.