The published work submitted herewith involves the application of Relevance theory (as a theory of verbal communication) to the description of Galician and Spanish, and to translation. The phenomena studied within these areas are examined from the point of view of language use. This allows us to see them together as instantiations of language and thus as being theoretically and fundamentally of a kind. As a result, they are also subject to the same principles of communication. The theoretical approach used and applied throughout is that of Relevance theory. This approach allows for an explanatory theory of verbal communication, which encompasses the two areas under study and thus provides a unitary theoretical framework to account for the phenomena examined. The various aspects of language description and translation explored here are therefore seen as instances of verbal communication to be studied precisely under a single general theory (and not as instances of different fields that should be examined by different theories). This submission is structured in three parts. The first part involves an introduction to the publications submitted, which includes a brief literature review. This review provides an overview of the most important approaches to communication, including the code mode, the Gricean approach and the approach adopted here, namely, Relevance theory. This introductory part also includes a discussion of the overall coherence of the publications submitted, together with their impact and contributions in the wider context of the field of study. The second part of this submission deals with applications of Relevance theory to the description of Galician and Spanish in a range of areas, including prepositional direct objects, presuppositional effects, interpretive use of language, and non-declarative sentences. In all these cases, current approaches are reviewed and critiqued, and alternative accounts are provided as applications of the theoretical framework provided by Relevance theory. The third and final part of this submission deals with applications of Relevance theory to translation in a number of areas, including interlingual interpretive use of language, interlingual enrichment, interlingual impoverishment, and degrees of acceptability in translation. One of the main themes in common between all these areas is the notion of discrepancy between original and target texts in translation. It is shown that many of these translation discrepancies arise from the gap found in verbal communication between what is encoded and what is communicated. Some of the most important types of gap that exist in verbal communication are examined in detail and their impact on translation explored throughout.