Scholars often address the process of enlargement as one-sided argument. This work provides a general theory of organizational expansion by including strategies and actions of both, applicant states and members of international organizations. It is argued that dependent on the domestic characteristics of states an organization strategically implement a set of conditions to avoid the application and admission of states, which are either not able to conform with the rules or not willing to pay the costs of membership. This process incorporates two stages. I test this theory by utilizing a Heckman-Probit-Selection Model, which accounts for this two-stage procedure. The results confirm that conditions are important to avoid costs in the process of expansion.