A Semantic Desktop is a means to manage all personal information across application borders based on Semantic Web standards. It acts as an extended personal memory assisting users to file, relate, share, and access all digital information like documents, multimedia, and messages through a Personal Information Model (PIMO). This PIMO is build on ontological knowledge generated through user observations and interactions and may be seen as a formal and semi-formal complement of the user’s mental models. Thus it reflects experience and typical user behavior and may be processed by a computer in order to provide proactive and adaptive information support or allows personalized semantic search. The Semantic Desktop is build on a middle ware platform allowing to combine information and native applications like the file-system, Mozilla, Thunderbird or MS-Outlook. In this talk I will show how machine learning techniques may be used to support the generation of a PIMO. I will further introduce the main concepts, components, and functionalities of the Semantic Desktop, and give examples which show how the Semantic Desktop may become reality.