This thesis aims to improve tool support for personal information management (PIM) by developing a better understanding of PIM behavior and needs from a cross-tool perspective. The research objectives are to systematically investigate integration as a design strategy for improving PIM tools through developing cross-tool requirements, designing and implementing a novel integration mechanism, and evaluating its effectiveness. The contributions will include improved knowledge of cross-tool PIM behaviors, a WorkspaceMirror prototype, evaluation results of the prototype, and design and methodological recommendations for developing improved PIM tools.