In order to define a shared reference towards a harmonization of methods and tools used in a European Network of Living Labs we developed the interoperability cube for harmonizing Living Labs. We derive this from the assumption that when we focus on those elements that Living Labs want to exchange with each other, we have an appropriate basis for harmonization of methods and tools. Each of the sides of the harmonization cube facilitates interoperability between the phases of a Living Lab and organizational, technical, and contextual aspects. The problem of bridging methods and tools from one Living Lab to another becomes considerably simpler if the two Living Labs in question share a common model; put differently, whether the methods and tools used are harmonized.