This chapter deals with interoperability among pervasive networked systems, in particular accounting for the heterogeneity of protocols from the application down to the middleware layer, which is mandatory for today's and even more for tomorrow's open and highly heterogeneous networks. The chapter then surveys existing approaches to middleware interoperability, further providing a formal specification so as to allow for rigorous characterization and assessment. In general, existing approaches fail to address interoperability required by today's ubiquitous and heterogeneous networking environments where interaction protocols run by networked systems need to be mediated at both application and middleware layers. To meet such a goal, this chapter introduces the approach that is investigated within the Connect project and that deals with the dynamic synthesis of emergent connectors that mediate the interaction protocols executed by the networked systems.