The tsunami simulation software TsunAWI is based on unstructured finite element meshes, utilizing a linear Lagrange conforming and non-conforming finite element numerical discretization method. TsunAWI is used for scenario computations in the German-Indonesian Tsunami Early Warning System (GITEWS) as well as for hazard assessment studies for local disaster management authorities in Indonesia. The early warning system, developed in the GITEWS framework is introduced under the special focus of the role of simulation. Starting from the non-linear shallow water equations for wave propagation, the discretization method in TsunAWI is described. Some remarks on mesh generation and the inundation scheme follow. The evaluation of an operational model, like TsunAWI, is an important issue and is outlined by examples. Finally some applications like hazard assessment for Padang and inundation mapping for Bali are given.