This book presents the first in-depth investigation of modality in Galician linguistics, offering a theoretical discussion of modal categories and a fine-grained description of epistemic adverbs. The first half of the monograph deconstructs the most relevant approaches to modal categories and shows how the traditional concept of modality is a problematic notion, how it relates to other concepts such as evidentiality and mitigation, and how it ought to be conceived of in order to become a more useful instrument for linguistic analysis. A new way of understanding modality is explored and illustrated through Galician examples. The second half of the book zooms in on six epistemic adverbs, which are exhaustively studied from both a formal and a functional perspective. Combining a quantitative and a qualitative perspective, the book shows that adverbs make up a rich semantic scale and establishes several factors that condition their occurrence in discourse, challenging previous conceptions of this grammatical domain.