The purpose of this Master's thesis is to develop a context-specific substantive theory of trust building based on the experiences of development workers in Laos, as well as the methods they identify as keys to a better partnership. The research material is based on eleven interviews with civil society development workers in Vientiane, Laos. The study context is partnerships between in-country International Non-Governmental Organizations and local Non-Profit Associations. Grounded theory methods were used to collect, code and analyze the data. From the data categories emerged and were generated into a substantive process model describing how partnership trust is built over time through relationship building. The substantive process model shows three sub-categories of trust- building which are building relationships, maintaining relationships and moving forward together. These sub-categories entail both parties to approach one another with an openness to differences and adaptation to change, flexibility, investing in the relationships, being vulnerable and forming good structural frameworks with good communication and cooperation. This study indicates that social relationships, between organization workers, increases trust which is essential for an effective partnership.