 Constrained and unconstrained fibring, being categorial, are universal constructions, and so enjoy well-defined and theoretically predictable formal properties. Profiting from universal constructions, in order to handle algebraic fibring, it is enough to define appropriate categories of signatures and logic systems. Indeed, the same fibring construction (coproduct or cocartesian lifting) can be performed in different categories of logic systems. This is a remarkable advantage of the categorial perspective for fibring. There are several proposals in the literature devoted to combining logics presented in different ways by means of algebraic fibring: propositional Hilbert calculi, sequent and hypersequent calculi, first-order modal logics, higher-order modal logics, non-truth-functional logics, logics semantically presented through ordered algebras (encompassing generalized Kripke models) etc.