A significant amount of personal information is received, stored and reused on a daily basis. Although we organise our information in various ways, we frequently face problems in re-finding information at a later point in time. The problem of organising and re-finding information is addressed by multi-disciplinary research in the field of Personal Information Management (PIM). While various tools for PIM~activities, such as file explorers or cloud-based services, exist for a long time, they introduced the problem that information becomes fragmented across these tools. Further, we still often use digital and physical media in a simultaneous way during everyday tasks. Nevertheless, existing research has mainly focussed on the design of PIM tools for either the digital or physical information space, often neglecting the simultaneous use of digital and physical documents.

In this dissertation, we take a cross-media approach to PIM application design where the digital and physical information spaces are unified. We introduce the vision of Cross-Media PIM User Interfaces which foresee a seamless transition across both information spaces during re-finding activities. Additionally, we aim for synergy between user interface design and a user's current organisational behaviour and re-finding strategies. In order to enable the design of cross-media PIM user interfaces, we have defined a number of user-centric as well as technical requirements. These requirements are based on our gained insights into a user's organisational and re-finding behaviour as well as the design of prosthetic memory helping users during their re-finding activities. In a second phase, we have developed the Document Tracking (DocTr), Context Modelling Toolkit (CMT) and User Interface Management (UIM) software frameworks to track, manage and display the necessary document metadata and the corresponding organisational structures. This metadata is needed to offer support for the re-finding mechanisms of a user's organic memory. The UIM framework is also responsible for the seamless transition between the digital and physical information spaces. The presented software frameworks enabled the design of different cross-media PIM user interfaces such as the PimVis visualisation that can interact with the file explorer and augmented ring binders as well as an augmented physical filing cabinet which can be controlled via a tangible user interface. Our proof-of-concept user interfaces have been used as study platform in two exploratory user studies. The results of these studies validate our three proposed main design principles including the support for a seamless transition between information spaces and the synergy with a user's current organisational behaviour as well as the re-finding mechanisms of the organic memory. We also gained further insights into the design space of cross-media PIM user interfaces where we show that users use different re-finding cues across the digital and physical information space, that user interfaces are best integrated in a ubiquitous way in a user's organisational environment and that users aim to be in control of the integration of the user interfaces in their environment where self-development of the interactions between the user interfaces is crucial. This dissertation presents the foundations for a new generation of PIM solutions that work in synergy with the user and brings up some essential design questions for future cross-media PIM solutions.