Augmented reality (AR) and mediated reality (MR) systems have shown to allow experts to virtually be at any place in the world without traveling and to interact with local users to solve complex problems. In combination, AR and MR technologies can be used to merge the shared perceived realities of different users as well as enriching their own individual experience. For example, difficult construction problems can be solved, training on complex machinery can be performed under expert supervision, or experts can guide challenging surgery. This workshop addresses the above vision. The goal is to bring together researchers who are interested in collaboration in merging realities. The participants will then build a large picture of research on collaboration in AR and MR as well as set up a common research agenda for work going forward. This, in turn, can be used to build a research community.