In recent years, a growing number of organizations have outsourced logistics services to logistics services providers (LSPs). Consequently, the outcome of logistics outsourcing is significant in determining the outcome of contemporary supply chains. To account for greater interconnection between organizations, supply chain relationship is crucial for achieving successful logistics outsourcing. Because organizations need to continuously change their decision-making in outsourcing, relationships among organizations in outsourcing are dynamic. Further, because logistics outsourcing has created more SCRs among suppliers, LSPs, and customers, managers need to use a network perspective to manage multiple relationships in the process of outsourcing. The triadic relationship is recognized as the smallest network structure. Researchers have therefore suggested that studying triadic relationships can help expand the knowledge of managing network structures in supply chains. As a result, the primary goal of this research is to study dynamics of supply chain relationships in logistics outsourcing from a view of triadic relationship. This relationship is called a logistics triad and consists of a supplier, a logistics service provider (LSP), and their common customer. Balance theory is a theory that was specifically developed for studying triadic relationships. Balance theory has been used in this thesis as a theoretical lens to develop a conceptual framework and research propositions in order to study logistics triads. Because only a few supply chain studies have adopted balance theory so far, there is a lack of a well-designed research instrument to investigate the research target that the present study explores. To rectify this paucity, qualitative research was conducted using multiple case studies to explore why and how a logistics triad transitions between different triadic relationship structures. The present research was carried out in two stages. The first stage collected triadic cases from LSPs. To improve validity and reliability, the second stage used a deductive process to test findings of the first stage by collecting triadic cases from suppliers and customers. Results of the comparison between the two stages provided verified research findings because the two stages exhibited close similarity. In stage one, the findings indicate that balance theory on its own is insufficient to explain the stability and dynamics of logistics triads. This led to the identification of factors that influenced the relationship dynamics in logistics triads. Among these factors, the combined effects of purchasing volumes, resource capability, and focal firm can override influences from other factors to determine stability and dynamics of logistics triads. The influence from the focal firm demonstrates that the supply network model is more useful than balance theory to study logistics triads. Overall, this thesis makes four major contributions to the knowledge of supply chain relationships: developing an integrative model of triadic relationship dynamics, identifying control approaches used by organizations to dominate triads, comparison between balance theory and supply network model, and demonstrating organizations' mediating effects on dyadic relationships within triads.