© 2014 Dr. Bogdan Augustin Dicher ; This thesis is an investigation into logical pluralism. The main question it addresses is whether pluralism about logical consequence is compatible with the invariance of the logical constants’ meaning across different consequence relations. I begin by arguing that a model-theoretic approach to logical consequence is a sub- optimal setting for defending meaning-invariant pluralism. Subsequently, the pluralist thesis is recast on the basis of a proof-theoretic treatment of logical consequence. From this perspective, the issue of meaning-invariance boils down to the interplay between the structural properties and rules of a logic and its operational rules, which govern the behaviour of the logical constants. The centre stage of the analysis of the viability of meaning-invariant pluralism is occupied by the concept of harmony. I show that harmony does not force the adoption of monism about logical consequence. The analysis of the various proposed formal embodiments of harmony guides the approach to the issue of meaning-invariance. I argue that, when the relation between structural frameworks and operational rules is correctly characterised, none of the proposals provides a definitive argument against meaning-invariant pluralism. My own view is that the structural and operational levels of a logic stand in an Euhyphric relation. Just like structural properties determine some aspects of the constants’ behaviour, the constants themselves determine some of the structural properties of a logic. I argue that this Euthyphric connection is the key to stabilising the constants’ meaning across different consequence relations—if not completely ruling out meaning variance.