Interface (TSI), which directly interfaces with the underlying local operating system and resource management system. Security model The security within UNICORE relies on the usage of permanent X.509 certificates issued by a trusted Certificate Authority (CA). These certificates are used to provide a single sign-on in the UNICORE client, i.e. no further password requests are handed to the user. In addition the certificates are used for authentication and authorization, including the mapping of UNICORE user certificates to local accounts, e.g. Unix uid/gid, and for signing XML requests, which are sent over SSL based communication channels across 'insecure' internet links. Using X.509 certificates is one example for the consideration of well-known standards, e.g. released by the Global Grid Forum (GGF), within the UNICORE architecture. For trust delegation, UNICORE uses signed SAML assertions, while local authorisation is controlled by XACML policies. Licensing All components of the UNICORE technology are open source software under BSD license and can be downloaded from the SourceForge repository. UNICORE in research & production Many European and international research projects base their Grid software implementations on UNICORE, e.g. EUROGRID, GRIP, OpenMolGRID, VIOLA, or the Japanese NaReGI project. These projects extended or are extending the set of core UNICORE functions, including new features specific to their research or project focus. The goals of such projects are not only limited to the computer science community. Other scientific domains such as bioengineering or computational chemistry are also using UNICORE as the basis for their work and research, like in the OpenMolGRID or Chemomentum projects. Within the European DEISA project leading HPC centers in Europe joined to deploy and operate a pervasive, distributed, heterogeneous, multi-tera-scale supercomputing platform. UNICORE was used as the Grid middleware to access the DEISA resources. UNICORE is deployed in distributed computing infrastructures in Europe (PRACE, the European Grid Infrastructure EGI) and is foreseen to be deployed in the upcoming Extreme Science and Engineering Discovery Environment (XSEDE) infrastructure in the United States. UNICORE is successfully used in production environments, e.g. within the John von Neumann-Institute for Computing (NIC) to access the 294912 core "JUGENE" IBM BlueGene/P supercomputer and the 26304 core "JUROPA" cluster. The users of these resources come from a broad field of scientific domains including e.g. astrophysics, quantum physics, medicine, biology, computational chemistry, and climatology. References I. Foster, C. Kesselman (Eds.), The Grid: Blueprint for a New Computing Infrastructure, Morgan Kaufmann Publishers Inc. San Francisco, 1999. D.