We have performed density functional theory (DFT) calculations of the atomic and electronic structures of ethylenediamine on Ge(100). The two amine groups in ethylenediamine can interact with germanium surface atoms through a N-H dissociative nucleophilic reaction and/or N-dative bonding with an electron-deficient down Ge atom. Of the monodentate and row-bridged bidentate structures that formed, the dative-bonded configurations were found to be more stable than the NH dissociative adsorption structures. The formation of row-bridged bidentate, structures is more favorable than that of on-top or end-bridged structures. In simulated STM images, the three types of row-bridged adsorption structure have characteristic features, and the row-bridged dative-bonded configuration gives rise to features due to both adsorbed ethylenediamine molecules and the underlying Ge atoms.