Financial institutions want to participate in the digitization services demanded by consumers. “Banking-as-a-platform” is an increasingly popular business model. By way of this business model, traditional banks and fintechs move from a fully controlled environment, with a full end-to-end product or service without external service suppliers, to an environment where consumers are directly connected to third parties. The role of a platform is to connect different user groups; users who offer products or services via the platform are called producers, and users in need of the services or products are described as consumers. The research agenda of McIntre & Subramaniam (2017) addresses the need towards a more comprehensive view of design choices related to networks, platforms and strategy. Often network effects are mentioned as the most important reasons to introduce openness. It is unknown whether for platforms in banking, expected network effects have an impact on the choice for level of openness. It could be that network effects have an essential part herein, perhaps this is not the case, maybe there are also other factors that have impact. Therefore, this research will explore the impact of expected network effects on the choice of the platform to become more open, or not. The choice will be approached from the sponsor perspective and the provider perspective since these roles are both involved in strategic design choices on openness and related network effects. The purpose of this research is to contribute to a structured overview of possible positive and negative impact of openness in the financial sector, and thereby contribute to the knowledge base. More specifically, the research provides insight into whether openness is included in their platform strategy and if expected network effects have impact on the choice of being open in this specific sector. The scope has been narrowed because the financial sector encompasses a large variety of services and institutions. This research focuses on the (sub) sector of traditional banks with the ambition to implement the “banking-as-a-platform”. The described area of the financial sector is labelled as the Purple Banks. One Purple Bank and one connected retail platform has been selected for this case study. The platform in this research is referred to as FinCo. A case study method is used because this in dept research method allows for a deeper understanding of underlying mechanisms. To give direction to the possible impact of openness in the case study, a frame of reference indicating possible impact of platform openness is needed. In this research a theoretical framework is constructed. The theoretical framework provides an overview of possible positive and negative impacts. The theoretical framework is not suitable for immediate use, it is too generic. Therefore, it is made specific by adding 7 propositions on the financial domain resulting in a theoretical framework specified on the domain. The theoretical framework specified on the domain is used as a frame of reference to identify possible positive and negative impacts of openness. Semi-structured interviews are used to gather data on the possible positive and negative impacts of openness identified by the sponsor and provider of a platform in the financial sector. The result is a framework with only relevant propositions for the specific case study, referred to as overview of factors found in the case study.