The UNICORE grid system provides a seamless, secure and intuitive access to distributed grid resources. In recent years, UNICORE 5 is used as a well-tested grid middleware system in production grids (e.g. DEISA, D-Grid) and at many supercomputer centers world-wide. Beyond this production usage, UNICORE serves as a solid basis in many European and International research projects and business scenarios from T-Systems, Philips Research, Intel, Fujitsu and others. To foster ongoing developments in multiple projects, UNICORE is open source under BSD license at SourceForge. More recently, the new Web services-based UNICORE 6 has become available that is based on open standards such as the Web services addressing (WS-A) and the Web services resource framework (WS-RF) and thus conforms to the open grid services architecture (OGSA) of the open grid forum (OGF). In this paper we present the evolution from production UNICORE 5 to the open standards-based UNICORE 6 and its various Web services-based interfaces. It describes the interface integration of emerging open standards such as OGSA-BES and OGSA-RUS and thus provides an overview of UNICORE 6.