This chapter seeks to understand inter-organizational-trust as an antecedent factor in the adoption of and participation in e-commerce. Exploratory research from different theoretical perspectives including the inter-organizational relationship theory, transaction cost economics theory, resource dependency theory, and a literature review on trust in business relationships, and trust and security based mechanisms paved the way to the development of a conceptual model. The model was tested via four case studies consisting of a large public sector organization and three Small-Medium Enterprises (SME) involved in customs clearance. SME included an Internet service provider, a customs broker (agent) and an importer. Data was collected via in-depth interviews, discussions with key personnel, and from existing documents. The findings suggest that there are two forms of trust; trust in the technology and trust in the trading partner. Further, the findings strongly indicate that inter-organizational-trust is important for e-commerce participation, as organizations need to cooperate, collaborate and communicate timely and relevant information in order to facilitate e-commerce. This entails not only technological proficiencies, but also trust between trading parties, so that business transactions are sent and received in an orderly fashion.