Combined logics are essential for reasoning about complex systems. In this work we analyze three mechanisms for combining logics (synchronization, parameterization and fibring) and show how they can be represented in the context of the theory of institutions by exploring the connections between them. For the purpose we adopt the notion of heterogeneous specification as a structured specification in a suitable Grothendieck institution, as proposed by R. Diaconescu. The talk reports ongoing joint work with C. Caleiro e J. Ramos.