In recent history, computational devices evolved from simple calculators to now pervasive artefacts, with which we share most aspects of our lives, and it is hard to imagine otherwise. Yet, this change of the role of computers was not accompanied by an equivalent redefinition of the interaction paradigm: we still mostly depend on screens, keyboards and mice. Even when these legacy interfaces have been proven efficient for traditional tasks, we agree with those who argue that these interfaces are not necessarily fitting for their new roles. Even more so, traditional interfaces preserve the separation between digital and physical realms, now counterparts of our reality.During this PhD, we focused the dissolution of the separation between physical and digital, first by extending the reach of digital tools into the physical environment, followed by the creation of hybrid artefacts (physical-digital emulsions), to finally support the transition between different mixed realities, increasing immersion only when needed. The final objective of this work is to augment the experience of reality. This comprises not only the support of the interaction with the external world, but also with the internal one. This thesis provides the reader contextual information along with required technical knowledge to be able to understand and build mixed reality systems. Once the theoretical and practical knowledge is provided, our contributions towards the overarching goal of merging physical and digital realms are presented. We hope this document will inspire and help others to work towards a world where the physical and digital, and humans and their environment are not opposites, but instead all counterparts of a unified reality.