The Grid is considered as a crucial technology for the future knowledge-based economy and science. The Wisdom Grid project (a joint research effort of the University of Vienna and the Vienna University of Technology) aims, as the first research effort, to cover all aspects of the knowledge life cycle on the Grid - from discovery in Grid data repositories, to processing, sharing and finally reusing of knowledge as input for a new discovery. This paper first outlines the architecture of the Wisdom Grid infrastructure and then focuses on the kernel architecture component called Grid-Miner, which realizes the knowledge discovery, based on data mining and On-Line Analytical Processing (OLAP) in Grid repositories. A running GridMiner prototype is already available to the scientific community as an Open Service System.