This paper studies internal organization of a firm using an incomplete contracting approach a la Grossman-Hart-Moore and Aghion-Tirole. The two key ingredients of our model are externalities among tasks that require coordination, and investment in task-specific human capital. We compare three types of organizational structures: centralization where the decision authority for all tasks is given to the party without task-specific human capital, decentralization where the decision authority for each task is given to the party with necessary human capital, and hierarchical delegation where the decision authority is allocated in a hierarchical fashion. Centralization is optimal when externalities and the requisite coordination are the main issue...